Technical Information

G-1 High-Quality Die Molding Manufacturing Technology

G-1 High-Quality Die Molding Manufacturing Technology

Die manufacturing technology has changed from copy-machining or trace machining to advanced machining with the integration of CAM systems, solid work models and virtual software. Machining for automotive dies is especially demanding since they require complex profiles and demand high productivity. Recently, with our introduction of high-efficiency production technology that uses the best of our newest control technology we have been able to make machining that is much more efficient and cost effective. In this section, we would like to introduce you to our lineup of high quality, highly productive and highly efficient technologies using the newest CNC control advancements.

[Platform]
G. Manufacturing technology based on features of molds
[Applications]
Machine tools

[Technical points]
CNCSHAPE function: Function for machining the high-quality surface efficiently by internal calculation of part data.  with a special triangular tool.

  • SF function: Control of tool peripheral speed for change in slope of machined surface.
  • Zone machining function: Machining by designating a zone when the zones with different machining conditions are present.
  • Rapid traverse circular interpolation function: Return time can be shortened by 28%.
  • In-corner machining: Cutting of a pocket hole with a special triangular tool.

1. Introduction

For the die manufacturing, the memory size for machining data (programs) is ever-increasing and CNC systems for machine tools are also evolving accordingly. Taking the CNCSHAPE function for example, it pre-reads large-size data during machining and performs internal calculation of machining data so that a high-quality machined surface can be produced. By fully utilizing this CNCSHAPE function, the following functions are available now.

  1. SF function using the tool peripheral speed control.
  2. Zone machining function that allows the setting of different machining conditions for each of the specified zones.
  3. G00 rapid traverse circular interpolation function (G00 circular interpolation function).
  4. In-corner machining function that allows the cutting of a pocket hole corner.

2. CNCSHAPE function

2.1 SF function

Fig. 1 Change in the peripheral speed of the cutter edge with change in profile

Fig. 1 Change in the peripheral speed of the cutter edge with change in profile

A ball end mill used for machining a die is ball-nosed, and peripheral speed of the cutter edge changes with the cutter position used for machining. That is, as the cutter position is nearer to the center of revolution axis of the ball end mill, the diameter of the cutter edge decreases and the peripheral speed slows down. When the free-form surface of the die is machined with this ball end mill, the peripheral speed of the cuter edge currently used for machining is always changing because the spindle speed of the machine remains unchanged. In machining of a sharp-sloped area as shown in Fig. 1, the diameter of the cutter edge is large and the peripheral speed becomes fast. In the machining of a gentle-sloped area, the diameter of the cutter edge is small and the peripheral speed drops.
Currently, to make change in the slope of such a machined surface, the SF function calculates an angle of inclination for each block based on the Z-axis travel distance in relation to the X-axis and Y-axis travel distances and commands the revolution speed and feed rate as per the results of calculation of the ball end mill contact diameter (i.e., diameter at the cutting point) to maintain the specified cutting speed.

Fig. 2 SF function verification model

Fig. 2 SF function verification model

Table 1 compares the machining time when the SF function verification model as shown in Fig. 2 is machined according to the previous machining conditions and the machining conditions using the SF function.
[Machining conditions]
Material: Cast iron (FC300)
Cutter used: R15 ball end mill
(Feed distance per one revolution of cutter is kept constant.)

 As known from Fig. 2 above, when the SF function is used, the spindle speed and feed rate change according to the slope of the machined surface. Thus, the machining time has dropped by 29% and quality of the machined surface has been improved on its flat area. For the cutter also, wear of the cutter edge has decreased and the service life has extended.

Table 1 Comparison of machining conditions
Machining methodPreviousSF machining
Spindle speed S (min-1)25005000
Feed rate F (mm/min)2500Proportionate to cutter edge radius.
Machining time62 min. 40 sec44 min. 30 sec.

The time for shuttling the cutter by 100 over the SF function verification model in Fig. 2 was calculated.

2.2 Zone Machining Function

Fig. 3 Setting of tool recessed zone, and die intermixed with SKD-11 insert material

Fig. 3 Setting of tool recessed zone, and die intermixed with SKD-11 insert material

Sometimes, a pocket hole for a slide block exists on the machined surface of a die or a different material is laid under the machined surface. If this zone is machined with the same tool, the tool will be damaged and machining efficiency will deteriorate, which are issues yet to be solved for the machining of dies. Normally, when the machining conditions differ as stated above, machining is executed by creating different part programs. As a result, machining quality will deteriorate due to steps, etc., or the machining time will increase.
The zone machining function specifies a zone in the machining range, which has different machining conditions from the other machining range, and selects relevant machining conditions designated beforehand when the tool enters the specified zone. This function can affect an override on the programmed feed rate and spindle speed according to the programmed conditions. Additionally, it is possible to specify the shift value so that the tool can be retracted in the Z-axis direction in the specified zone, well addressing the machining with the tool recessed from the non-polished surface. (See Fig. 3)

Fig. 3 shows an example of machining different kinds of materials. By changing the machining conditions of the different material (SKD-11) laid in the die, quality of the machined surface has been improved and the number of polishing processes has been slashed. The zone machining function is effective for machining the following parts.

  1. Area where machining load is increased as in the pocket machining.
  2. Area where vibration is likely to occur by the use of a long tool..
  3. Area where a material of different kind is laid.
  4. Vertical wall area of highly rigid material, etc.

2.3 Rapid traverse circular interpolation function

Fig. 4 Rapid traverse circular interpolation function

Fig. 4 Rapid traverse circular interpolation function

When machining a profile of die, etc., the tool path is generally unidirectional or reciprocating (shuttle).
In the unidirectional machining, high-quality machined surface can be assured because the machining direction is the same. As the tool has to return to the machining start position, however, the machining time will increase.
In shuttle machining, the machining time is short and machining efficiency improves. Repetition of climb cutting and conventional cutting, however, will easily cause steps between the adjacent tool paths to deteriorate the quality of the machined surface. To obtain the high-quality machined surface, therefore, unidirectional machining is selected together with the rapid traverse circular interpolation function to speed up the return motions of the tool.
his function allows automatic creation of a circular interpolation command on the machine control side, even if the tool is programmed to return at rapid traverse in the previous unidirectional machining. The operation of this function is exemplified in Fig. 4 When the rapid traverse circular interpolation function is used, circular interpolation is executed automatically at the corner of the return tool path, which results in minimized waste time for acceleration or deceleration and reduction in machining time. When this function was used in the profile machining in Fig. 2 above, the return time could be reduced by 28%, compared with that of the previous technique.

2.4 In-Corner Machining

Fig. 5 Pocket hole machining

Fig. 5 Pocket hole machining

When a pocket hole is machined with an end mill as shown in Fig. 5, the corner is machined with the radius R of the cutter. In prior machine processes, the only way to machine the area left by the R corner required an additional or secondary operation called E.A.M. machining or "Electrical Discharge Machining". This process required an electrode made per the machining profile and of course the time to design and finally manufacture.
The in-corner machining feature eliminates the need for an additional processor when cutting such a corner. It uses a special triangular tool and the machining cycle is shown in Fig. 6.

Fig. 6 In-corner machining cycle

Fig. 6 In-corner machining cycle

As shown above, this function cuts the corner by synchronous control of tool revolution and each feed axis. In the cutting operation, the machining time is less than that of EDM machining. The cutting feed is slow and the tool life expectancy is diminished which consequently creates another area for improvement.

3. Conclusion

Efficient machining of a quality die is possible by combining the die machining functions that we have introduced above. The die has a large number of inclined holes for slide pins and water line holes for cooling, However, high-efficiency machining of these holes is also essential to reduce the machining time. There are many issues still remaining that have yet to be improved for die manufacturing, and we will make every effort to develop the machining technology for realizing high-efficiency and process-intensive die manufacturing and to enhance the machining technology.