Examination of two categories of manufacturing machines within Glasgow University’s Mechanical Engineering Workshop.
Identical clamp components were manufactured by each category of machines. This highlighted key differences in the manufacturing process
- Individual task machines: milling, turning, grinding, cutting and drilling.
- CIC Flexible Machining Cell: Bridgeport VMC – fully automated and performs variety of machining operations. Ability to mill, drill and tap on four axes. (less space, higher maintenance cost, economical for high volume of product output)
Tools, Work Handling and Set Up Times
The tools used in each cell are similar and perform the same tasks on the clamp
Set up speed:
- Conventional cells required calibration of machine and zeroing of axes after each tool change.
- Bridgeport VMC tools spacial position on set of axes is calculated by machine, therefore it starts machining without taking time calibrating position of the tool.Work handling:
- Conventional systems require manual operation to manufacture products (could result in human error, less accurate machining or greater tolerances applied).
- Fully automated systems – operator only required entering program to a computer then securing the material before starting the process. Higher accuracy is achieved compared to human operation.
Fully automated system only required the material to be moved from a store to the CIC machine, where it could be fully fabricated within the system.
Conventional cells required a variety of material movement. Most of the material’s time when being manufactured was spent waiting to be gauged, transported between machines and set up on these.
Speed of Machining
The Bridgeport VMC tools are able to be changed automatically within the machine during a machining job, taking only seconds between individual tasks, reducing periods of no work. Precision was acquired easily and at high speed as the dimensions were programmed beforehand.
In comparison the conventional cells required manual changing between tools. Machining was slower, especially when trying to stay within the tolerances.
Research When Selecting Cutting Materials
General Unstable Materials
Carbon Tool Steels: Can produce sharp edges, soft compared to other materials, but inexpensive.
High Speed Steels: Inexpensive, hard at moderate temperatures (up to 67 HRC). Sharp cutting edges.
General Stable Materials
Carbides: Reasonably espensive, high abrasion resistance (HRC 90)
Ceramics: Chemically inert, resistant to heat, desirably in high speed applications, extreme fragility. Reasonably inexpensive.
Diamond: Extremely expensive. Hardest material available. Unsuitable for steel machining. Fragile.
Types of Tools
Diamond, carbides and ceramics usually used. Tools come in a variety of shapes depending on the application that they will be used for.
Carbides or high speed steels are used. Often milling tools have a cutting edge across all the end part of the tool so they can be plunged into material such as end mills. For the Bridgeport VMC a standardisation exists within the milling tools.
High Speed Steels are widely used with helix shaped cutting tool on the end of the shaft.