Planning can lead to cost savings when designing fixtures
January 17, 2011
Too often, specifying clamps for a fixture in an automated welding cell is an afterthought. That slight can lead to unnecessary costs and complexity.
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The electric shovels P&H Mining manufactures, such as this one loading copper-bearing ore into a material hauler, can weigh up to 1,200 tons. The dippers on the largest trucks can gather up to 100 tons of material in one swoop. Photos courtesy of P&H Mining Equipment, Milwaukee.
To say that specifying clamps for automated welding applications is an afterthought in North America might be an understatement. That would suggest that design engineers are thinking about them at all.
The reality is that most design engineering effort is focused on the actual creation of the component, not its design for manufacturability. As a result, the component design gets kicked downstairs to the shop floor, and only then is the robotic welding fixture considered. That’s where the focus may finally fall on the clamps. The engineer tries to force a clamp to fit the design of the fixture instead of finding the optimal and most efficient clamp and designing the fixture around it.
By overlooking the impact of properly specified clamps for an automated welding fixture, manufacturers might be incurring unneeded costs and sacrificing user-friendliness. These tips can help a design engineer deliver a better fixture for the folks responsible for manufacturing metal components.
European manufacturers understand this approach. When tackling a fixture design for a component, the European engineer is thinking of how the part should be held down and what the best way is to accomplish that task. They are more likely to incorporate standard componentry for the fixture rather than building the fixture and possibly putting themselves in a situation where they need a special clamping design, one not found in a catalog.
The phrase “special request” means additional expense associated with creating the unique clamp and more days required for delivery. In today’s world where any cost saving is significant and lead-times are measured in days and not weeks, specifying special designs for a clamp could be considered overkill.
That why it’s important to take a more holistic look at fixture design. That leveling foot the metal component might be sitting on is just as significant as the final product. The commitment to quality needs to begin before the first assembly steps are taken. The way to achieve this quality and make it repeatable is to take complexity out of the process, and that calls for basic and functional fixtures with standard clamps.
Of course, special requests can be accommodated. If a clamping arm, for example, needs to be made longer or configured in a different way, the change can be made. It, however, can’t be delivered as quickly as a stock item.
Time is money, and spending extra time trying to adjust clamps on a fixture is time the manufacturer is not getting paid for. That’s why the clamps need to be easy to adjust.
This isn’t a marketing pitch. Lean manufacturing principles dictate that steps be taken to reduce setup time between fabricating activities. Even the simplest of improvements, such as the move to a clamp that can be adjusted easily with a couple of twists of an Allen wrench, can save seconds, which add up quickly over multiple shifts.
For example, Figure 1 shows a miniclamp that is fastened to the mounting through the cylinder. This can be changed quickly without losing the original placement.
Quick-change features aren’t the only things that make a clamp user-friendly. The design can be a huge assistance as well. When pneumatic connections need to be made, for example, clamps are now being designed with connections at the underside base of the clamp (see Figure 2). This keeps the tubes out of the way of the welding robot and enables the clamps to be fastened through the collar.
Even the presence of a welding robot can’t prevent the metal in a fixture from absorbing the stresses associated with the electric arc. That’s why clamps need to be able to withstand the stresses of the welding process.
Clamps made from high-strength or treated steel are the best candidates for the job. Those made from aluminum or cast iron won’t hold up as well.
A Teflon® finish, which prevents weld splatter from sticking to a clamp, is also available for most clamps.
It’s not out of sight, out of mind. However, if a clamp is out of sight, it’s also likely out of the way of the welding robot and the torch head.
Any additional room afforded the welding robot reduces the chance of a collision with the fixture, a situation that manufacturers want to avoid at all costs. Clamp designs can be incredibly small, yet don’t give up any clamping force. In fact, a clamp as small as 40 mm by 205.5 mm is able to produce as much as 3,000 newtons of clamping force.
Contrary to the typical thoughts of someone in charge of purchasing items for a welding fixture, a clamp is not a one-time cost. The purchaser needs to think about all costs associated with that clamp throughout the component’s useful lifetime.
For example, a pneumatic clamp works in conjunction with an air compressor, and energy is needed to power the air delivery to the clamps. An inefficient clamp design can lead to much more air consumption than is necessary. In some instances, a new clamp can draw as much as 50 percent less air, which is a significant savings if the purchaser looks at each clamp in a fixture and its air consumption over a year’s time.
The buyer also should take a look at the way clamping force is delivered. A clamp with roller bearings (see Figure 3) likely will last much longer than one that relies on bushings.