Getting it together

Automotive Design & Production, June, 2004

As there is an increase in the use of assemblies consisting of different materials, there is a challenge to put these materials--say aluminum and steel--together so that there are such things as:

* The required dynamic and/or static strength

* Reproducibility of joints

* No damage to coatings or the materials' surfaces

* The possibility of automating the process.

While there are some people who are deploying spot welding or laser welding for these tasks, according to the people from TOX[R]-PRESSOTECHNIK (Warrenville, IL; www.tox-us.com) there are some issues that need to be addressed with the welding processes, including:

[ILLUSTRATION OMITTED]

* Complicated clamping fixtures

* Material compatibility

* Surface thermal damage

* High energy requirements

* High equipment investment

* High maintenance requirements.

Another alternative is to use rivet and screw fastening systems. Here the concerns are along the lines of:

* Part preparation

* Special tooling and equipment requirements

* Large quantities of additional material

* Appropriate material selection to avoid galvanic corrosion.

Then there is the approach developed by TOX-PRESSOTECHNIK, the TOX-Round-Joint clinching system, a cold-forming process that joins two or more sheets with a simple punch-and-die combination that can be used in a manual or automatic setup. One example of where it is being used is for the hood of the Peugeot 307. The hood consists of two aluminum sheets--1-mm and 2-mm thick--and includes a 1.5-mm thick steel hood latch assembly. To produce the assembly there are four robotic units and 10 stationary units. Each of the TOX-Round-Joints formed require 80 kN of press force. Two of the guns are tasked to forming the nine 8-mm joints for attaching the latch to the hood while the balance assemble the sheets.

Another application in development is being pursued by Ford at Cologne, Germany. They've conducted tests using the TOX joining system for producing wheels with two different types and thicknesses of steel: a DPW600 material 3.65-mm thick and a HR45 that's 2-mm thick. Forty wheels, size 6.5J X 16 in., are being tested for the Ford Mondeo. The joints are 12 mm in diameter and the die depth is 2.4 mm. The press force used was 150 kN. The shear strength of the joints proved to be 12,800 N and the peel strength 5,800 N. The joints proved to be equal to spot welds in bending and rolling tests on the wheels. The results of the joining process were 100% above the minimum strength values required by Ford.