By optimizing the entire metal cutting process, it is possible to achieve high productivity and profit margins in the machining operation. The basis of this work is the intelligent application of cutting tool parameters, while making full use of the machine tool's machining capabilities. Achieving effective machine tool utilization contains two important components. The first is to find a way to maximize the amount of time that the machine can be used for cutting metal, and the second part includes making this time effective, and the second part includes making this time effective, reliable, and profitable.

Maximize available time

The full utilization of machine tools must start with maximizing the time that they are available to cut metal. Even though a machine is in the shop 365 days a year, its production availability is reduced by the time taken each year for holidays and other activities. This leaves approximately 1,300 or 1,400 machine hours available for production. Even so, the machine is not cutting metal for all of this time. Programming and set-up will take a certain amount of time. To keep non Produktive time as short as possible, manufacturers should adopt a strategy that includes off-line programming and a modular design approach. Tool libraries and automatic tool changers speed up the other time-consuming event of tool handling. Automated work handling and exchange workstations help reduce the time required to load the raw workpiece and unload the completed parts. Time saved by increasing programming speed, speeding up set-up methods and simplifying tooling and work handling can be used to machine parts.

Make efficient use of time

After implementing a strategy to maximize cutting time for metal, the problem faced by manufacturers is how to make efficient use of this time to produce as much product as possible at the lowest cost. The key is to make full use of the machine tool functions when the cutting edge is in contact with the workpiece material. It is also very important to understand the limitations of the machine tool functions.

When formulating plans to utilize available time more effectively, it is apparent that certain elements of the machining process cannot be changed. The end use of the machined workpiece determines the material that the manufacturer should select, and the machinability of the material points to the initial cutting parameters that can be used. For example, titanium alloys have poor thermal conductivity, which requires the use of low cutting speeds and feed rates to minimize heat generation. The machine tool capabilities are also fixed, as changing machines is not typically a straightforward option. The manufacturer realizes these factors when assessing production costs. However, if the machine tool characteristics are evaluated in accurately and the resulting cutting conditions are not sustainable, then the resulting cost discrepancy between the expected and actual costs can be significant.

When determining all the initial cutting parameters of the machining, some general rules need to be followed. It is necessary to select the appropriate depth of cut and feed rate to avoid tool breakage, ensure the formation of the required chips, and limit heat generation. Cutting speeds that are too high will cause the tool to wear rapidly, while speeds that are too low will prevent the tool from working efficiently.

Fast cutting generally results in parts in a shorter time. While the machining time is reduced, the tool life is also reduced and the tooling cost will be higher. More tooling will be required to complete the job and the down time required for tooling changes and relocations will increase the overall operating cost. Fast cutting, while it results in a higher machining cost, can be balanced with slow cutting, which has a lower operating cost. A stable production efficiency and process stability lies somewhere in between the two methods: insufficient cutting parameters will reduce the cost, but the tooling cannot operate efficiently and productivity will suffer; while ever increasing parameters will increase productivity, but the tooling will quickly wear or break.

In addition, the selection of machining conditions is not only a function of the cutting tool, but in most cases, it is also a function of the capabilities of the machine tool. Different machine tools have different power, torque, speed, and stability limitations. The obvious limitation is power.

Ratings alone do not determine the machine’s function for a specific application. A 60-kW metalworking machine would appear to be powerful enough, but if it is intended to fabricate a 12-m-long, 3-m-diameter roll, 60 kW is not enough. The power required to machine a specific workpiece depends on the workpiece material and its dimensions, the depth of cut, the feed rate, and the cutting speed. Because cutting forces increase exponentially with increased speed, the power requirement will increase.

Therefore, high cutting speeds may require power in excess of the machine rated power.

In addition, extreme cutting parameters may exceed the capacity of other functions of the machine tool. Cutting depths that are too high can produce forces that exceed the rigidity of the machine tool structure, and vibration may reduce the quality of the parts. Similarly, very high feed rates can produce large amounts of chips that can interfere with the cutting process and block the chip removal system.

To make a greater degree of utilization of the machine tool within its functional limits, it is necessary to apply an intelligent, balanced approach to the development of cutting parameters. This usually involves reducing cutting speeds, while correspondingly increasing the feed rate and depth of cut. The use of the largest possible depth of cut, considering the stability of the machine tool, can reduce the number of passes, and thus shorten the machining time. The depth of cut usually has a minimal effect on tool life, but the cutting speed has a significant effect on tool life. On the other hand, although extreme feed rates have a negative effect on the surface finish of the workpiece, the feed rate should still be increased to a greater degree.

When the supplier has achieved a reliable combination of feed and depth of cut, the cutting speed can be used to fine-tune the machining. The objective is to use cutting conditions that provide a productive metal removal rate and process stability. A good combination of machine performance and cutting parameters can achieve a balance between tooling cost, process stability, and productivity.

Future Strategy

If it is realized that machine tool performance can limit the machining process, replacing the machine tool is not a simple, quick or economical solution. Changing the application parameters of the cutting tool to make the existing machine tool perform better is a faster and simpler way. A relatively long service life of the equipment is also an important consideration, even if the investment in the new machine tool is feasible. A company may purchase a machine tool that is matched to or exceeds its current needs, and over the next five, ten or more years, factors such as part workpiece material, size and volume can and will change significantly, while the machine tool can still operate normally. To address these changes, it is necessary to change the cutting conditions in a more intelligent way.