Linear Chain Takes the Heat at BMW Mini
The capabilities of the Linear Chain Actuator from R. A. Rodriguez have assisted Wokingham based Maypole Engineering in the design and manufacture of a turnkey conveyor and oven system for the main BMW Mini wiring loom. Its compact design and ability to operate without pneumatics helped ensure the success of the project. In fact, the system could become a BMW standard – Maypole reports it now has enquiries for further systems from South Africa, China and the Netherlands.
Wiring looms manufactured in Europe for the BMW Mini production lines at Cowley in Oxfordshire arrive in blue harness bags. However, a problem was identified with the looms arriving in winter. Due to the cold weather, some components; due to the loom temperature within the bag, became damaged during assembly. As each wiring harness is for a specific car, damaged components mean scrap looms.
“We were approached by BMW to tender for a system that would gently heat the looms to make certain parts more pliable and fit for assembly,” explains the company’s Managing Director, Stuart MacSwan. “Our successful proposal was based on a 9m oven system with a powered, push chain driven conveyor that would allow BMW to heat 20 bags simultaneously in a 20 minute timeframe – thus delivering a one minute production cycle time.”
Maypole devised an automatic chain loop system within the oven to meet the criteria. The loading end is a manual feed system that allows the pallets to be returned to the load area after the harness heating bag has been delivered to the vehicle. The basis of the transportation system relies on a Linear Chain Actuator from R. A. Rodriguez.
“We’ve used this product from R. A. Rodriguez before and they work well,” says Mr MacSwan. “For this application our casing is mounted vertically and therefore the product is a compact solution. The product allowed extended linear motion for very small space requirement. Furthermore, being electrically driven it eliminated the need for pneumatics, which is a huge advantage in a system like this.”
In its magazine, the chain is stored spirally within a narrow chamber making the Linear Chain ideal for applications demanding long strokes where space is at a premium. The device provides high positioning accuracy, constant stroke speed and shock-free motion with no elastic hysteresis under load. It has been designed for a long operational life and minimal maintenance.
The pushing application on the oven system at BMW Mini requires a 1m transfer, which is completed in four seconds. Each bag with wiring harness weighs around 25kg. The oven system heats the bags at a temperature of 60°C, allowing the nominal core temperature within the bag to rise by 11°C.
“The results of the heating system have been welcomed by BMW Mini UK as the warm wiring loom is now far easier to install in the vehicle,” says Mr MacSwan. “What’s more, location grommets that had been difficult to fit previously now pop into place with ease.”
The system was installed at Cowley in the summer of 2013 and it has been working without issues for three shifts a day ever since. As a result of the success, other BMW plants have since made enquiries that could see the system become standard at this automotive giant. According to Mr MacSwan as many as four or five further systems could be commissioned in the next year or so. The system adheres to all safe working standards and can be applied to any size of harness heating bag.
Linear Chain is available in three basic sizes allowing stroke lengths of up to 5m and a maximum push force of up to 35,000N.