Pneumatic Brake Redesign

The term project for my Product Design class was novel - for the first time, a select few teams would be working with companies to improve their products. Our team was assigned to work with a local corporation on their pneumatic disc brake modules used in web tension control applications. I was team leader for this project.

Exploded View - Final Assembly

Start to Finish

This photo shows sort of a timeline of our project: on the far left is the customer's original body. Next is their assembled product. In the middle is our 3-D printed prototype. 4th is the first attempt at machining the body, where the threads failed to mate. On the right is our completed prototype!

Cut Away View

This cut away section view shows how the components are arranged inside the body.

Subassemblies

Here, the threaded subassembly and piston assembly are outlined to show how everything fits together. Also highlighted are the air inlet holes.

Function Analysis Chart/BOM

This chart lists all the parts for the final assembly, categorizes them (standard, custom, or unchanged from the customer), and briefly describes their functions. Notice that many parts/assemblies still have multiple, coupled functions. However, decoupling all functions would be very difficult and would likely result in a very expensive product. Good design requires compromise.

FEA of Press Fit

We wanted to make sure the threaded insert could handle the stresses of the press fit, so we did a quick static FEA to verify stresses were in normal limits.

CNC Machining the Body

Check out that coolant flow!

CNC Machining the Body

Press Fitting the Threaded Assembly

The piston assembly goes inside, on top of a gasket for maximum sealing.

Press Fitting the Threaded Assembly

This is the pipe section we used to distribute the load onto the ring.

Fully Assembled!

Disassembled

If there is a problem with leaks, the threaded assemblies from each side can be tested individually. If the leak is coming from the subassembly, it can be discarded individually, while saving the body (the most expensive part).

Jig for Machining the Body

We made this jig from scrap aluminum and some dowel pins so that we could clamp the body down to drill the air inlet holes at the correct angle.

Air Inlet Holes

The feature where the hole emerges is extremely thin. We did not measure properly the first time and ruined a part... But we learned from our mistakes and nailed it the second time!

Overview

The Product

The customer makes web tension control products for facilities that process materials that come on rolls. Their disc brakes, load sensors, and control systems form a closed feedback loop to continuously monitor and adjust the tension in the web for proper web control. Our group focused on one family of their pneumatic disc brake modules. The brake modules in the family all use the same body, and have different configurations of piston assemblies and friction pads. One module has a piston assembly on one side; another module has piston assemblies on both sides. The third brake consists of two single sided brakes aligned and facing each other such that their pistons extend towards each other to apply force to a central disc. This is the opposite of the double sided brake where the pistons expand out to apply force to two connected discs.

The Problem

The customer's design relies on a press fit operation to create the airtight seal necessary for proper functioning of the brake. A ring is press fit around the piston assembly and into the body to assemble and seal the product. Therefore, the press fit has two functions: to assemble the product, and the create the airtight seal. This dual dependence is called function coupling. Function coupling is undesirable according to the principles of axiomatic design. In this case, function coupling was giving the customer trouble because of the fact that press fits are permanent. So in order to check the module for leaks, it had to be assembled. However, once it was assembled and a leak was discovered, it could not be disassembled to fix or diagnose the leak, and thus was discarded. Our goal was to address this problem in our design.

The Solution

Our original plan was to do a failure mode analysis of the assembly to determine the origin and the cause of the leaks, then design and prototype an improved brake using that knowledge. However, a failure mode analysis, redesign, and construction of a prototype were not reasonable with such a short timeline. We decided instead to implement a turn-key solution by designing a fully compatible brake module which decoupled the functions of final assembly and airtight-ness.