Metalforming Electronics



Die Designs and Sensor Wiring

By: George Keremedjiev

Monday, August 1, 2011

There are two preferred procedures to hide and protect electronic sensor wiring as it routes from die sensors to the centralized connector junction box, to avoid cut, frayed, crushed and otherwise non-functional wires. Here we will discuss retrofitting sensor wiring within existing dies compared to working with new die designs.

New Die Designs

The best time to think seriously about the most effective s to route sensor wiring is during strip layout. Careful analysis of the proposed layout and the subsequent die-design phases will uncover the various required progressive functions. A thorough set of failure-mode explorations of these progressive functions will then uncover likely problem areas, including short or long feeds, part-ejection confirmation, slugging, cam returns, punch breakage, nitrogen-cylinder leakage and pad-return failure. To conduct such a careful analysis, the die designer must consult with toolroom and pressroom personnel, including the company’s sensor specialist. Let’s call this group of inhouse consultants the error-proofing team (EPT). Each team member brings to the table their unique perspectives and concerns as the die designer moves from basic strip layout to actual tool design.

Imagine that the strip layout, tooling-design phases and parallel consultations with the EPT leads to a set of predicted failure modes that include several separate zones within the die, each of which will require electronic sensing. Sensing might include stripper monitoring for slug detection, monitoring of a spring-loaded lever for over/under feeds, and sensing of cam-return motions and part out.

Each of the targeted areas within the die will house electronic sensors, with cables in need of protection. The die designer must specify sensor-cable channels to be milled in the lower die plate during die construction. These channels should be deep and wide enough to contain the sensor cables, yet not so deep and wide as to compromise the integrity of the lower die plate. The channels also must include drain holes to avoid buildup of oil and coolant, and cover plates that can be screwed in place. One approach is to mill the channels with steps so that the cover plates sit on top of the channels flush with the surface of the lower die plate.

In cases where the exact location of the sensors is unknown, the die designer should route the channels within a reasonable distance of the sensor locations. Often a simple H-pattern for the channels suffices. In fact, several shops use this pattern on every die, regardless of sensor placement.

Retrofitting Existing Dies

Trying to protect sensor wires within an existing die often proves much more difficult and time consuming than does working with a new die. One common solution is to use steel hydraulic brake-line tubing to protect exposed sensor cables. Hydraulic tubing generally features a thick wall that resists denting and crushing. The tubing comes in various diameters, allowing the designer to route several sensor cables within one tube.

Just as the channel approach in new die designs requires that the channels be routed precisely to the sensor locations, the hydraulic tubing must be formed in a tube bender into the required shapes necessary to route the wires around tooling sections. The die maker connects tubing sections using inline, elbow or T-shaped fittings. To clamp the tubing to the lower die plate, the die maker can employ simple C clamps screwed into place.

Good sensor-cable protection practices, as outlined above, can extend the lives of sensors to match the run life of the tools in which they are embedded. Remember—if the sensor wire is exposed, odds are it will be cut, crushed or frayed. Why take the chance? MF


Related Enterprise Zones: Sensing/Electronics

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