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HIGH SPEED MACHINING
ABSTRACT
Over the past 60 years, high speed machining (HSM) has been applied to a wide range of metallic and non-metallic work piece materials including the production of components with specific topography requirements and machining of materials with hardness of 50 HRC and above.
With most steel components hardened to approximately 32-42 HRC, machining operations currently include:
Rough machining and semi-finishing of the material
Heat treatment to achieve the final required hardness
Machining of electrodes and electrical discharge machining of specific parts of the dies or moulds
Finishing and super finishing of surfaces
In leading industrial countries, in die and mould manufacturing, a significant portion of the lead-time is spent for machining and polishing operations .Therefore the machining and polishing portion of dies and moulds takes approximately two third of total manufacturing costs. If the quality level after machining is poor and if cannot meet the requirements there will be varying need of manual finishing work.
Machining with high speeds (HSM) is one of the modern technologies, which in comparison with conventional cutting enables to increase efficiency, accuracy and quality of work pieces and at the same time to decrease costs and machining time.


INTRODUCTION
Over the past 60 years, high speed machining (HSM) has been applied to a wide range of metallic and non-metallic work piece materials including the production of components with specific topography requirements and machining of materials with hardness of 50 HRC and above.
With most steel components hardened to approximately 32-42 HRC, machining operations currently include:
Rough machining and semi-finishing of the material
Heat treatment to achieve the final required hardness
Machining of electrodes and electrical discharge machining of specific parts of the dies or moulds
Finishing and super finishing of surfaces
In leading industrial countries, in die and mould manufacturing, a significant portion of the lead-time is spent for machining and polishing operations .Therefore the machining and polishing portion of dies and moulds takes approximately two third of total manufacturing costs. If the quality level after machining is poor and if cannot meet the requirements there will be varying need of manual finishing work.
Machining with high speeds (HSM) is one of the modern technologies, which in comparison with conventional cutting enables to increase efficiency, accuracy and quality of work pieces and at the same time to decrease costs and machining time.
DEFINITION OF HSM
The first definition of HSM was proposed by Carl Salomon in 1931.He assumed that At a certain cutting speed which is 5-10 times higher than in conventional machining, the chip removal temperature at the cutting edge will start to decrease.
The figure below illustrates his definition. There is a relative decrease of the temperature at the cutting edge that starts at certain cutting speeds for different materials.
Fig.1 chip removal temperature as a result of the cutting speed
Actually there are many different ways to define HSM, upon them HSM is said to be,
¢ High cutting speed machining (Vc)
¢ High rotational speed machining (n)
¢ High feed machining (Vf)
¢ High speed and feed machining
¢ High productive machining
Finally, HSM is a powerful machining method that combines high feed rates with high spindle speeds, specific tools and specific tool motion.
Figure below shows the generally accepted cutting speeds in high speed machining of various materials.
Fig.2 High cutting speed ranges
ADVANTAGES
Major advantages of HSM are high material removal rates, the reduction in lead times, low cutting forces, dissipation of heat with chip removal resulting in decrease in work piece distortion and increase part precision and surface finish.
Low cutting force gives a small and consistent tool deflection. This in combination with a constant stock for each operation and tool is one of the prerequisites for a highly productive and safe process.
Cutting tool and work piece temperature are kept low which gives a prolonged tool life in many cases.
As the depths of cut are typically shallow in HSM, the radial forces on the tool and spindle are low. This saves spindle bearings, guide ways and ball screws.
The contact time between the cutting edge and work piece, must be extremely short to avoid vibrations and deflection of the wall. The feed is faster than the time for heat propagation.
Reduction of production process as hardening, electrode milling and EDM can be minimized. This gives lower investment costs and simplifies the logistics.
The figure below illustrates the above statement
Fig.3 Improvement of production process when using HSM
A) Traditional process. The steps are:-
1) Non-hardened (soft) blank
2) Roughing
3) Semi finishing
4) Hardening to the final service condition
5) EDM process-machining of electrodes and EDM of small radii and corners of big depths
6) Finishing of parts of the cavity with good accessibility
7) Manual finishing
B) Same process as A, where the EDM- process has been replaced by finish machining of the entire cavity with HSM thereby reduction of one process step
C) In this process,
1) Initially the blank is hardened to the final service condition
2) Roughing
3) Semi finishing
4) Finishing
5) Manual finishing.
Here the HSM most often applied in all operations and thereby reduction of two process steps. Normal time reduction compared to the process A is approximately equal to 30-50%
The other benefits include reduced material handling cost, lower residual stress, increased productivity, possibility of machining of very thin walls, enhanced damage tolerance, shortened delivery times, elimination of coolant and increased cutting efficiency etc.
Table.1 below shows the various effects due to the above features which positively impact the global manufacturing process chain with in a machine shop.
Features Effects
Reduced heat transfer in to the work piece Part accuracy
Reduction of cutting forces Part accuracy, surface quality
Increased cutting speed Stability of rotating cutting tool feed rate, increased material removal

Table.1
Graph below shows that the cutting force (Fc) decreases with increase in cutting speed (VC).
Fig.4 Fc vs. Vc for a constant cutting power of 10kw
APPLICATION AREAS OF HSM
High speed machining is being mainly used in three industry sectors due to their specific requirements.
The first category is industry which deals with machining of aluminum to produce automotive components, small computer parts or medical devices. This industry needs fast metal removal because the technological process involves many machining operations.
The second category which is aircraft industry involves machining of aluminum parts, often with thin walls
The third industry sector is the die mould industry which requires dealing with finishing of hard materials. In this category it is important to machine with high speed and to keep high accuracy. In this industry HSM is used to machine such parts as
Die casting dies: This is an area where HSM can be utilized in a productive way as most castings dies are made of demanding tool steels and have a moderate or small size.
Forging dies: Most forging dies are suitable for HSM due to their complex shape. The surface is very hard and often prone cracks.
Injection moulds and blow moulds: These are also suitable for HSM, because of their small sizes. This makes it economical to perform all operations in one step.
Milling of electrodes in graphite and copper: It is an excellent area for HSM. Graphite can be machined in a productive way with Ti(C,N) or diamond coated solid carbide end mills.
Modeling and prototyping of dies and moulds: This is one of the earliest areas for HSM. Easy to machine materials such as aluminum are used. The cutting speeds are often as high as 15000-50000 rpm and the feeds are also very high.
Using of the HSM in the above mentioned regions can cause the reduction of production process when electrode milling ECM and EDM. HSM ensures a dimensional tolerance of 0.02 mm, while the tolerance when using ECM is 0.1-0.2mm and EDM 0.01“ 0.02. Replacing ECM with machining causes the durability and tool life of the hardened die or mould is increased considerably.
HSM- MACHINING SYSTEM
MACHINE TOOLS
In HSM, various configurations of machine tools are being used. However 3-axis horizontal and vertical milling centers (HMC and VMC) are most configurations. Al though vertical machining centers have disadvantages concerning chip removal, they are the less expensive choice and therefore, are presently more widely used than horizontal machining centers. CNC 4-axis milling offers the option of tilting the milling cutter to improve the cutting conditions. Five axis machines with interchangeable spindle units allow to rough, semi finish and finish with a single set up. It also allows the machining of work piece having large diameter.
Below are some typical demands on the machine tool and the data transfer to HSM (ISO/BT40 or comparable size, 3-axis)
¢ Spindle speed range <=40000 rpm
¢ Spindle power >22 KW
¢ Programmable feed rate 40-60 m/min
¢ Rapid travels <90 m/min
¢ Block processing speed 1-20 ms
¢ High thermal stability and rigidity in spindle
¢ Air blast/coolant through spindle
¢ Advanced look ahead function in the CNC
CUTTING TOOLS
Among the cutting tools used for machining castings and alloy steels carbide is the most common tool material. Carbide tools have a high degree of toughness but poor hardness compared to advanced materials such as cubic boron nitrite (CBN) and ceramics. In order to improve the hardness and surface conditions carbide tools are coated with hard coatings such as titanium nitride (TiN), Titanium carbonitride (TiCN) and titanium aluminum nitride (TiALN) and recently with double/soft coatings such as MOVIC. Other cutting tool materials are Ceramics (AlO, SiN), cermet and poly crystalline diamond (PCD).
In general tools ranging from 0.5 to 1.5 inches inn diameter carbide insert tools with TiCN coatings are significant for the materials with less than 42 HRC, while titanium aluminum nitride coatings are used for materials with 42 HRC and over. However depending on application, materials and coatings for the best performance vary. High speed cutting application for such tool materials and coatings can be classified as
¢ CBN and SiN for cast iron
¢ TiN and TiCN coated carbide for alloy steel up to 42 HRC
¢ TiAlN and AlTiN coated carbide for alloy steels having hardness 42 HRC and over.
For special applications especially for hard turning (HRC 60-65) PCBN inserts with appropriate edge preparation are also successfully used.
.
NEED OF COATED TOOLS
Hard coating applied to cutting tools can significantly alter the properties of the tools. Low coefficients of frictions and low tendency to adhesion of the coating to the work piece material will result in less heat generation during the cutting operations. The low thermal conductivities of the coating will generate a thermal barrier on the tool surface. Less heat will be transferred to the tool and thus a major part of the generated heat will be transported away from the cutting areas with the chips. In addition high thermal stability, hot hardness and oxidation resistance resistances will reduce the wear of the tool.
SOME RECOMMENDED PARAMETERS FOR HSM
1. TRUE CUTTING SPEED
As cutting speed is dependent on both spindle speed and diameter of tools, HSM should be defined as true cutting speed above a certain level. The linear dependence between the cutting speed and the feed rate result in high feeds with high speeds.
Fig.5 Cutting speed
Where ap = axial distance from the tool tip to the reference point
n = spindle speed
De = effective diameter
2. MATERIAL REMOVAL RATE
The material removal rate, Q is consequently and considerably smaller than in conventional machining with the exception when machining in aluminum other non ferrous materials and in finishing and super finishing operations in all types of materials.
Where Vf = feed speed
ae = step over distance
3. SURFACE FINISH
Like in conventional machining the surface finish in HSM is determined by conditions like the cutting tool geometry, coating of the cutting tool, wear status of the cutting tool, lubrication, cutting strategy determined on the CAM system, cutting tool extension, work piece material etc. Assuming all these parameters are controlled, the surface finish to be expected may be calculated through the following approach.
Where Rth = theoretical surface roughness
D = diameter of cutting tool
ae = step over distance
Since the maximum cutter diameter is often limited by the part geometry, Rth only can be minimized by decreasing the step over distance
4. TOOL COST AND MACHINING COST
When introducing HSM, cost of cutting tools will increase significantly. The benefit of HSM is given by a reduction of processing time and cost, better surface finish, reduction of manual finishing work, better accuracy etc. For this reason cutting tool cost should only be seen as an integral part of the overall cost accounting. Machining cost will be less than the conventional machining process due to elimination of process steps, reduction of process time etc.
COMPARISON
Table.2 gives the comparison between conventional and high speed machine
CONVENTIONAL MACHINE HIGH SPEED MACHINE
Maximum speed 600 m/min
Maximum speed ~40 ipm
Require high levels of coolant Speed starts at 600 m/min
Feed starts at 100 ipm
With coolant, feed rate can go more than 2000 ipm
No feed for coolant for low feed rate.
Table.2
Table.3 comparison between speeds used in conventional machining and HSM using some selected materials
Table.3
Table.4 gives the comparison between conventional machining and HSM process
CONVENTIONAL HSM
The contact time between the cutting edge and work piece is large Contact time between the cutting edge and work piece is short
Less accurate work piece More accurate work piece
Cutting force is large Low cutting force
Cutting fluid is required Cutting fluid is not required
Low surface finish High surface finish
Material removal rate is low Material removal rate is high

Table.4
Table.5 gives the comparison between high speed machining (HSM) and electronic discharge machining (EDM) process
HSM EDM
Material removal by interference between tool and work contact process Non contact process
Dimensional tolerance 0.02mm Dimensional tolerance 0.1-0.2
Material removal rate high Material removal rate low

Table.5
DISADVANTAGES
¢ Need for expensive and special machine tools with advanced spindles and controllers
¢ Excessive tool wear.
¢ The higher acceleration and deceleration rates, spindle start and stop give a relatively faster wear of guide ways, ball screws and spindle bearings which leads to higher maintenance cost.
¢ Emergency stop is practically unnecessary! Human mistakes, hard ware or software errors give big consequences.
¢ Good work and process planning necessary.
¢ It can be difficult to find and recruit advanced staff.
CONCLUSION
¢ HSM is not simply high cutting speed. It should be regarded as a process where the operations are performed with very specific methods and production equipment
HSM is not necessarily high spindle speed machining. Many HSM applications are performed with moderate spindle speeds and large sized cutters
HSM is performed in finishing in hardened steel with high speeds and feeds often with 4-6 times conventional cutting data
HSM is high productive machining in small sized components in roughing to finishing and in finishing to super finishing in components of all sizes
Even though HSM has been known for a long time, the research is still being developed for further improvement of quality and optimization of cost.
REFERENCES
¢ A.O.Stevenson, High speed machining, SEARCH the industrial source book, vol.11.No.2,pp 49-52, 2003
¢ Ashley.S, High speed machining goes main stream, mechanical engineering, pp 56-61, May 1995
¢ Plaza.M, The prons and cons of high speed machining, Canadian machinery and metal working,pp8-10, September 1995
¢ Fall bohmer.P, H.K.Nakagawa, Survey of the die and mould manufacturing industry, Journal of materials processing technology,pp59,158-168,1996

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Machine tool spindle units

A B S T R A C T
This paper presents the state-of-the-art in machine tool main spindle units with focus on motorized spindle units for high speed and high performance cutting. Detailed information is given about the main components of spindle units regarding historical development, recent challenges and future trends. An overviewof recent research projects in spindle development is given. Advanced methods ofmodeling the thermal and dynamical behavior of spindle units are shown in overview with specific results. Furthermore concepts for sensor and actuator integration are presented which all focus on increasing productivity and reliability.

Introduction
Machine tool spindles basically fulfill two tasks:
_ rotate the tools (drilling, milling and grinding) or work piece
(turning) precisely in space
_ transmit the required energy to the cutting zone for metal
removal
Obviously spindles have a strong influence on metal removal rates and quality of the machined parts. This paper reviews the current state and presents research challenges of spindle technology.

Historical review
Classically, main spindles were driven by belts or gears and the rotational speeds could only be varied by changing either the transmission ratio or the number of driven poles by electrical switches. Later simple electrical or hydraulic controllers were developed and the rotational speed of the spindle could be changed by means of infinitely adjustable rotating transformers (Ward Leonard system of motor control). The need for increased productivity led to higher speed machining requirements which led to the development of new bearings, power electronics and inverter systems. The progress in the field of the power electronics (static frequency converter) led to the development of compact drives with low-cost maintenance using high frequency three-phase asynchronous motors. Through the early 1980’s high spindle speeds were achievable only by using active magnetic bearings. Continuous developments in bearings, lubrication, the rolling element materials and drive systems (motors and converters) have allowed the construction of direct drive motor spindles which currently fulfill a wide range of requirements.

Principal setup
Today, the overwhelming majority of machine tools are equipped with motorized spindles. Unlike externally driven spindles, the motorized spindles do not require mechanical transmission elements like gears and couplings. A motor spindle mainly consists of the elements shown in Fig. 2. The spindles have at least two sets of mainly ball bearing systems. The bearing system is the component with the greatest influence on the lifetime of a spindle. Most commonly the motor is arranged between the two bearing systems. Due to high ratio of ‘power to volume’ active cooling is often required, which is generally implemented through water based cooling. The coolant flows through a cooling sleeve around the stator of the motor and often the outer bearing rings. Seals at the tool end of the spindle prevent the intrusion of chips and cutting fluid. Often this is done with purge air and a labyrinth seal. A standardized tool interface such as HSK and SK is placed at the spindles front end. A clamping system is used for fast automatic tool changes. Ideally, an unclamping unit (drawbar) which can also monitor the clamping force is needed for reliable machining. If cutting fluid has to be transmitted through the tool to the cutter, adequate channels and a rotary union become required features of the clamping system. Today, nearly every spindle is equipped with sensors for monitoring the motor temperature (thermistors or thermocouples) and the position of the clamping system. Additional sensors for monitoring the bearings, the drive and the process stability can be attached, but are not common in many industrial applications.

Machine Tool Volumetric Accuracy?

Measuring machine performance

Allows process improvements before parts are made.

Allows predictive repairs of machines.


Why Improve
Machine Tool Volumetric Accuracy?

Measuring finished part dimensions

Can only be done after the part is completed.

Causes reject parts to be repaired or thrown way.

What are the Tools?

Machine Error Budgets
Machine Parametric Measurement

How did these tools evolve?

For over 90 years, the builders determined machine performance standards.

Dr. Georg Schlesinger recognized the need to do measurements on machine tools.

How did these tools evolve?

Schlesinger’s book, Testing Machine Tools, contains parametric tests, such as


limited to the characterization of machine spindles and moving components
roundness
straightness

How did these tools evolve?

Engineers at Lawrence Livermore National Labs found these methods inadequate for specifying their machines.

How did these tools evolve?

The ISO 230 Specifications were for the assembly of machine tool components not the capability of machines to make parts.

“parametric error budgeting”

“parametric error measurement”


What were their solutions?

They developed techniques to aid in specification, design & production of the world’s most accurate machine tools.

Identify machine axis relation parameters
Identify machine thermal error parameters
Identify machine environmental error parameters
Sum error parameters

Parametric Error Budgeting

Identify machine motion error parameters


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RECENT TRENDS IN MANUFACTURING – HIGH SPEED MACHINING
ABSTRACT
In recent years large amount of research has taken place to improve productivity in machining. One such research area developed to increase the metal removal rate is High Speed Machining (HSM). Machining of materials at four to six times the cutting speed used in conventional machining is called as High Speed Machining. The high speed machining technique has great economic potential due to high metal removal rate, better surface finish and ability to machine thin walls. The newer materials such as composite materials, heat resistant and stainless steel alloys, bimetals, compact graphite iron, hardened tool steels, aluminum alloys etc., needs this new machining (HSM). High speed machining offers a means to shorten delivery times boost productivity and increase profitability.
The aim of this paper is to give an overview of HSM and related technologies used in production systems for obtaining increased efficiency, accuracy and quality of finishing. A high speed machining center can reduce the need for polishing the surfaces of dies and moulds. It can produce EDM electrodes more efficiently. The high speed machining center also produces complex tooling competitively in a single setup. The HSM requirements, such as machine tool, cutting tools etc. are discussed in this paper. The application of high speed machining to die and mould machining is also presented.
1. INTRODUCTION
Machining of materials at four to six times the cutting speed used in conventional machining is called as High Speed Machining (HSM). HSM is one of the modern technologies, which in comparison with conventional cutting enable to increase the efficiency; accuracy and quality of the work piece and at the same time decrease the cost and machining time . The HSM technology allows the manufacturing of products with excellent surface finish with relatively little increase in total machining time. Carl Salomon conceived the concept of HSM after conducting a series of experiments in 1924-31. His research showed that the cutting temperature reached a peak value when the cutting speed is increased and the temperature decreases for a further increase of cutting speed (Figure 1). The increase in cutting speed demands a new type of machining system like the machine tool, cutting tool, CNC program etc. The use of high feed rate with high speed increases the metal removal rate, but the machine in turn requires lighter inertia tables, powerful motor drives and more responsive control systems. One definition of HSM states that, it is an end milling operation at high rotational speeds and high surface feeds. HSM normally uses a high speed in excess of 1000 m/min, feed rates above 1m/min and spindle speeds greater than 10,000 rpm.
1.1 Why High Speed Machining?
High material removal rates can be achieved by using high cutting speed, high rotational speed, high feed machining or high speed and feed machining. Practically it can be noted that HSM is not simply high cutting speed. It should be considered as a process where the operations are performed with very specific methods and production equipments. In many applications, HSM is used for machining the components with high spindle speeds and feeds for roughing to finishing and also for finishing to super finishing. In HSM the cutting tool and workpiece temperatures are kept low due to short engagement time. This normally increases the tool life. The increase of cutting speed decreases the cutting forces (Figure 2). The deflection of tool is kept less during cutting, which results in good surface finish (Ra 0.2 micron). The shallow depth of cut in HSM reduces the radial forces on tool and spindle. This increases the life of the spindle bearings, guide ways and ball screws.
1.2 Need for HSM Development
1. To survive in the competitive market, it is necessary to use HSM in order to reduce machining time and hence cost of production.
2. The newer materials such as composite materials, heat resistant and stainless steel alloys, bimetals, compact graphite iron, hardened tool steels, aluminum alloys etc., needs this new machining (HSM).
3. HSM offers high quality of products by avoiding manual finishing of dies or moulds with a complex 3-D geometry, aluminum thin walled component machining etc.
4. HSM eliminates the number of setups and simplifies the flow of material, which can reduce considerably the manufacturing throughput time.
5. HSM technique is one of the main methods in rapid product development.
2. HIGH SPEED MACHINING
The machining activity is an important component in the overall manufacturing. The HSM processes are increasingly used in modern manufacturing. However, such processes can lead to discontinuous chip formation that is strongly correlated with increased tool wear, degradation of the work piece surface finish, and less accuracy in the machined part. The variations of cutting force components are functions of chip load and cutting speed. The variations in cutting force produces severe self excited and forced vibrations which are detrimental to the tool life, work piece geometry, finish and finally machine tool itself .
2.1 Machine Tool for HSM
HSM has grown in popularity tool making industry. After an initial period of skepticism, high speed machining offers a means to shorten delivery times, boost productivity and increase profitability. The spindle is the most fundamental component of the HSM processes. In some cases retrofitting a faster spindle to a conventional machining center can realize some of the HSM benefits. The increased cutting speed, introduce dynamic stability problems into the machine tool components. This leads undesirable resonance in the machine parts, which require additional damping considerations in the design of machine tool components. A more accurate representation of high speed machining from a spindle design point of view is the DN number. DN is the spindle diameter in mm multiplied by the spindle speed in rpm. The commercial high-speed machines are available with DN number in the range of 1.5 million. The stability of the machines used for HSM become important to reduce the vibrations and chatter produced during machining. It was shown, that a substantial productivity gain as well as reduced vibration could be achieved by utilizing stability lobs in HSM machine tool design. One of the main objectives of HSM is high metal removal rate, which is achieved by using higher speed and depth of cut, particularly in roughing operation. Machining at surface speed higher than 915 m/min is more common in HSM and the chatter produced at that speed can be suppressed or avoided by either using an analytical model or an experimental technique or more desirably by a combination of both. The spindle dynamic characteristics at high speed were analyzed and observed that a spindle with angular contact ball bearings exhibits some change in dynamic stiffness as the speed increases. With the aid of computer aided modeling, the machine builders are able to analyze the machine dynamics and dynamic stiffness. The machine’s servo drives, spindle design and torque power curves are different for each application of HSM. The major development in HSM is correcting unstable machine conditions by a Chatter Recognition and Control System (CRAC). It is an on-line system for stabilizing the cutting conditions automatically by adjusting the cutting speed and feed. It uses the sound of the cutting operation, measured spindle speed and number of teeth on the tool to determine when chatter occurs and to automatically choose a new spindle speed. Winfough and Smith (1995) reported a new CRAC system as a tool in an NC program to use spindle speed and axial depth of cut combinations to obtain maximum metal removal rates.
2.2 Cutting Tools for HSM
The cutting tools are specially designed to suit HSM for high metal removal rate. All the cutting and holding tools used in HSM are to be designed for the specific purpose machining. The tools are normally provided with reinforced cutting edges by using either zero or negative rake angles. One typical and important design feature of the cutting tool is having thick core for withstanding maximum bending. The increased run-out error in the tool or tool holder reduces the life of the tool to a great extent. A method is described for changing the length of tool, so that the most stable region (machining condition) falls at the top speed of the spindle. Many different designs of tool–tool holder interface are developed to reduce the instability. Stability of the interface can be improved by shortening of the overhang portion and also using shrink fit tooling. The increased spindle speed limits the use of conventional taper interface provided with cutting tools. A modification has reported in traditional taper design to achieve more stiffness through face contact. The strong development of cutting tool materials and holding devices has increased the applications of HSM. Also the development of super hard cutting materials such as Cubic Boron Nitride (CBN), Poly Crystalline Cubic Boron Nitride for machining hard steel has created many new applications for HSM. Another development of tooling with exotic coating technologies is able to withstand the high temperature produced in HSM. In HSM the super hard materials as well as cutting edges resistant to high temperatures are the solutions for providing maximum performance for different category of materials.
2.3 NC Program for HSM
The productivity of a machine is always a concern for the machine developers and users. In conventional machining the increase of feed rate increases the productivity. But in most cases of HSM, the increase of the feed rate does not significantly improve the productivity. The productivity can be evaluated by calculating the productive and non-productive times. The productivity of the high speed machining centre depends directly on the quality of NC programs. A NC program was developed with a simulator to evaluate the productivity of the NC programs by considering an effective feed rate factor and a productivity factor. The effective feed rate depends on: (1) the command feed rate (2) the average per block travel of the tool (3) moving vectorial variation of the tool and (4) acceleration/deceleration or time constants. NC programmers must alter their overall machining strategy to construct tool paths to anticipate the cutting tool for its engagement with the work piece. Sharp turns and slow execution create jerky tool movements. This alters the load on the cutter, which causes tool deflection. This leads to reduced accuracy, surface finish and tool life. The servo controllers used in HSM many times failed to position the drives accurately. “Remaining stock analysis”–ability of the CAM system to know precisely where the stock is available after each cut, is used for predicting the constant cutter load. Experience has shown that tooling manufacturers and CAM software developers need to work closely together to ensure that the customers are able to get the major benefit from deploying new tooling technologies with optimized machining strategies. Using slower CAM software or a less powerful computer will lead to frustrating delays, with a new machine tool lying idle while NC programs are being generated (delcam). To perform HSM it is necessary to use rigid and dedicated machine tools and controls with specific design features and options. The machine should use advanced programming techniques with a more favorable tool path. The program should ensure constant stock for each operation. To achieve the above requirements the machine tool designers and engineers have been developing the machines for HSM with parameters specified below.

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