Hard Milling
In the last several years more and more manufacturers in the die/mold industry have reconized the growing need for there company to learn how to hard mill. I have worked for Single Source Technoligies and Makino for the last 5 years, They sell CNC milling and EDM machines in the Detroit area. Working for them I noticed that about 90% of the customers main focus was to buy equipment and tooling to start machining hard materials. Most manufactures rellied mainly on out sourcing to speciality shops or EDM departments to burn hard material. With the technology that SST/Makinohttp://www.singlesourcetech.com offers and some training there is no reason your company can't machine hard H-13, D2, S7, and CPM4 powder metals with HRC from 45-68.
What you need to start hard milling
Hard milling needs several items to make it work.
- Ridgid CNC mill
- High end CAM system
- Ridgid tool holders
- High end cutting tools
- The right training
All these components must come together to be successful in the machining of hard materials.
CNC Machining Center
- The CNC machining center is the most important part, the machine must be ridgid and have the ability to absorb vibration. The base construction comes into play along with a ridgid HSK spindle, also a CNC control that can process a lot of data to keep the machine running smooth. I worked for Makino so I know that there machines are designed for high speed/hard milling. They use a ridgid HSK spindle, with a Fanuc high speed look ahead (super GI) control. I had great success in hard mill demos with their machines. The machine should have digital drive technology with excellent acceleration and deceleration. This technology with the CNC control allows for accuracy, speed, and very little cutter ware.
- The Spindle is a important part of the machine, it must be ridgid and have the capibility of low end torque and high RPM's. The rigidity of the spindle has to do with the holder type, HSK interface should be used. The ridgidity comes from the way the hold fits in the spindle making contact on the spindle taper and the spindle face so there is no way for the holder to flex and vibrate, unlike the cat-40 or cat-50 hold that only make contact on a small portion of the spindle taper. The spindle should have ceramic bearings to reduce heat at high rpms and run out.
- As I talked about before the CNC control is an important part of the machine. It should be able to process data at a very fast rate. Makino uses the Fanuc 18I control with Makinos own high speed data processing called super GI4 or SGI4. What this does is looks ahead in the program 150+ blocks to maintain a smooth, fast running program.
CAD/CAM Software
- There are so meany CAD/CAM softwares out that have there own special nitch in there own market there are a few that are designed for hard milling like Graphical products CAM-Tool and Delcam's Powermill. No matter what software you use the strategies for making the toolpath are the same. The CAM software should be able to make a toolpath that keeps the tool in motion with no stopping, a nice continues flow is need to maintian a constant chip load. Also to maintian constant chip load the CAM software has to be able to use a stock model to know were extra stock is and remove it with extra paths if needed to maintian the chip load.
- When considering a part for hard milling you have to make sure that the CAD model is the best quality. Also the part itself hase to meet certian requirements. If there are areas that require more then a 5:1 diameter to length ratio you are going to have to do some experamenting to get the best results, this is were good training and tooling comes in to play.
Tool Holders
- There are several types of tool holders that can be used. As I said before the best type for hard milling is the HSK. They are the most ridgid because of the way it makes contact with the spindle face so there is no chance for flex. Click here to learn more about holder to spindle interface.
- Next you have to decide on the best tool to holder interface. There are side lock, collet, hydrolic, and shrink fit. For hard milling the best is by far shrink fit, because these tool holders are balanced and have the best ridgidity. precision collet and hydrolic holders are good for some type of applications.