How Does Workholding Make the Job Easier?
Introduction
Workholding refers to any device, including jigs and fixtures, used to securely position and firmly hold a workpiece in its proper orientation to the tooling with enough force to resist the forces of machining without deforming the part.
Better workholding makes the manufacturing job easier in many ways.
If put in place properly, workholding devices allow a machine to work at its full potential while efficiently and consistently producing quality parts.
In a recent Industry News Article “Introduction to Workholding,” Reid Supply describes the best way to ensure product quality in an industrial machining process.
There is no one-size-fits-all solution for workholding. The goal for manufacturers is to determine the best-fit combination of machining operations, automation and workholding devices. Working together, these goals maximize machine usage time, accommodate the need for automated changeovers, improve production throughput and lower manufacturing cost.
The choice of the most practical workholding solution to use generally depends on the shape, length, diameter, weight of the workpiece and the type of cuts required.
When mass production and automation are the end goals, the workholding strategy changes. For example, one primary goal during mass production is to keep the machines running as much as possible.
How Do Workholding Devices Make the Job Easier?
Workholding in all of its various forms makes the manufacturing job easier. Using jigs and fixtures that hold multiple parts make it easier by creating opportunities to:
- Reduce machine load and setup time
- Increase the number of parts per run
- Increase machine throughput
- Increase machine usage time
- Increase workpiece quality
Good workholding also makes it easier for the manufacturer to:
- Increase process automation
- Utilize robot loading and unloading of part pallets and individual workpieces
- Reduced operator fatigue
- Run lights out manufacturing overnight or during off shifts
- Increase speeds and feeds to accommodate complicated parts and new materials
- Allow 5-axis machines access to all sides of a workpiece in a single setup
Examples of Good Workholding Making the Job Easier
Workholding for Lathes
Since lathes typically turn cylindrical parts, they can often be held with the same style of workholding, including collets and hydraulic chucks. Mass-produced turned parts require additional equipment. One example is a bar feeder. As long as the stock size stays the same, many bars can be loaded into the feeder and are fed, bit by bit, into the lathe until they’re used up.
Lathes with production capabilities typically come with a parts catcher as well: usually, a small bin that that swings out on an arm to catch each part as they’re cut off. With short cycle times, a bar feeder, and a parts catcher, a powerful lathe can crank out hundreds or thousands of parts in a single “lights-off” period, without any human intervention.
Bar feeder set up to the left of a lathe
Workholding for CNC Machines
Workholding is often a complex, but necessary, problem to solve in manufacturing. CNC milling in production quantities or the milling of parts with complex profiles requires careful consideration of the workholding method to ensure maximum access to all sides of a workpiece in a single machine cycle.
Pallets and tombstones are one category of workholding, where multiple pieces of stock are prepared outside of the machine while it’s cutting another pallet or tombstone. They hold many pieces of stock and can be loaded into and out of a machine in seconds, often by loading onto a vacuum or other quick-change fixture. A pallet is a flat plate that holds many parts, while tombstones are typically large structures that rise off of the milling bed and hold parts on multiple sides.
Tombstones are common in 5-axis machines where the mill can easily access all sides of the tombstone. Horizontal mills and tombstones also lend themselves to mass production due to their advantage in chip control: instead of having to deal with chips falling all over the work in a vertical machine, chips fall right past the work and spindle in a horizontal mill.
A large array of modular tombstones
Workholding for Large, Complex or Delicate Workpieces
Some companies specialize in workholding technologies, such as Mitee-Bite. They create clamps and other products that make fixturing easy, even for very large or complex parts. These products are typically meant to work with t-slots, which are found in almost all milling machine tables.
Many other specialty workholding systems meet very specific needs. One unique example is a freeze-clamping system, which uses a very cold plate to freeze a delicate part to a surface, so it can be milled without using a potentially damaging clamping device like a machinist vise or other clamping method.
Freeze Clamping Device
Summary
Better workholding makes the manufacturing job easier in many ways.
If put in place properly, workholding devices allow a machine to work at its full potential while efficiently and consistently mass-producing quality parts.
The choice of the most practical workholding device to use generally depends on the shape, length, diameter, weight of the workpiece and the type of cuts required.
Finally, when Mass Production and Automation are the end goals, workholding strategies must change to make it easier to produce high-quality parts while keeping the machines running as much as possible and reducing manufacturing costs.