The base of a machine tool is critical to the performance of the machine tool. A large surface grinding machine may have a required positional accuracy of 0.005 mm on all axes. This accuracy must be maintained over the life of the grinder and during metal removal operations. Many components of the machine tool contribute to this accuracy. The base of the machine is the foundation upon which rests all other components in the grinding machine. Accuracy of the final machining operation on the machine tool base is required in order for the finished grinding machine to deliver the required 0.005 mm positioning accuracy. Use of a large CNC vertical gantry mill, like the Mitsubishi MVR43/49 Dx at K&M Machine-Fabricating Inc. is an economical and high quality method to achieve the required accuracy.
The purpose of the machine base in a machine tool is to provide a stable foundation for the operations that will be performed. The functions of the structure of the machine tool base are:
- Carry static and dynamic loads without distortion
- Assure that all moving parts are stable and move accurately
- Resist wear caused by moving parts
- Dampen vibration from machine tool operations
- Assure stability of the structure through the elimination of residual stress during construction
These functions of the machine tool structure are defined in Youssef and Hofy 2008 publication Machining Technology Machine Tools and Operations published by CRC Press in 2008 ().
The provider of outsourced machined steel fabrication services for large fabrications used in machine tool structures must take several steps to insure that the characteristics of the fabrication design are realized in the machine tool structure that is delivered to the customer. These steps include:
- Analysis of the customer requirements through review of drawings and specifications.
- Planning the manufacturing process.
- Sourcing of the steel plate and other materials.
- Cutting the steel plates to the design dimensions and tolerances and completing other secondary operations.
- Tack welding the structure to the in-process dimensions leaving material as required for final machining operations.
- Welding the structure to meet dimensional requirements and structural integrity requirements.
- Stress relieving the structure.
- Machining of the structure to meet dimensional requirements.
- Paint to the customer’s specification.
- Perform inspections.
The large vertical gantry mill is an ideal machine tool to perform the large machining that is required on a large grinder base. The Mitsubishi MVR43/49 Dx vertical gantry mill is large enough to handle the base in a single clamping. It is equipped with two right angle heads and a universal head. Using these heads it is possible to machine five sides of the work piece without moving the work piece. No variation in location or parallelism between features and surfaces will be induced by moving the fabrication between machining operations. Picture 1 shows a large grinder base during machining on the Mitsubishi MVR43/49 Dx vertical gantry mill.
Picture 1 – Large Grinder Base Machining
Typical tolerances required on a base for a surface grinder that is 8.2 meters long are 0.0013 mm flatness and 0.0025 mm parallelism between surfaces. The combination of process planning, machine tool, tooling, machine operation and quality system delivers the tolerances expected by the grinder manufacturer. K&M has two Mitsubishi MVR43/49 Dx vertical gantry mills installed along with nine other large vertical gantry mills. K&M specializes in contract machining of large structures to tight tolerances. A video of a Mitsubishi MVR43/49 Dx vertical gantry mill machining a large grinder base can be seen here. Picture 2 shows the large grinder base after machining and final paint.
Picture 2 – Large Grinder Base after Machining and Paint
K&M’s video showing Machining of Base Fabrication
October 21, 2014
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