Waste

Part 3

by Roger A.P. Fielding, BENCHMARKS

The waste which is to be found in most extrusion plants affects the facility’s ability to produce the right quantity and quality of extrusions—on time. The plant can’t meet delivery dates. So instead of delivering product to a customer at a specific hour of the day, it’s not unusual to hear of extruders who deliver on a particular day, or even within a particular week!

In addition to the causes of waste identified in the previous articles, the reasons for missing a delivery may also include the following: shortage of correct alloy, waiting for die delivery, waiting for die correction, dies in caustic, die “lost,” press broken down, no overtime, over-booked, or orders incomplete.

The late reports will also have notes listing the reasons for incomplete orders. And, it will be no surprise that the list will include references to the waste in the extrusion (finishing and fabricating) plant:

Metal: wrong billet size.

Dies: die broke, die plugging, or die lines.

Shortage due to scrapping metal at the press: poor surface, off shape, or off dimensions.

Shortage due to scrapping metal at the finish cut saw: runout table damage, cooling table damage, stretcher damage, batching or saw table damage, blisters, poor surface, off shape, off dimensions, wrong length, or poor transverse weld.

Material scrapped after ageing: failing properties (and any that were not caught earlier!)

All too often, the extruder ships material that is off-shape, has the wrong dimensions (including twist and bow), or surface damage, such as scratches, dents, and over-stretching, that was not picked up at the plant. (And by the time it reaches the customer the material may also have transportation damage.) “When a customer orders aluminum profiles from an extruder, he expects to pay for what he gets—and to get what he ordered. All too often, he gets a surprise package. There are limitless opportunities for improvement in extrusion management and technology that can result in far higher yield at better quality.”(1)

Waste has a direct impact on the bottom line, adding to the cost of extrusions, semi-fabricated and fabricated aluminum products. Waste increases the lead time between the receipt of an order and the delivery of a finished product. The extrusion plant that minimizes the lead time between order entry and delivery meets all its delivery schedules and is capable of turning its inventory twice each week.

Reducing Lead Time

From the above lists, it’s evident that the problems of controlling and reducing production lead time can be divided into five areas: billets, dies, machines, the extrusion process, and people. Rank the causes of production delays, then develop programs to correct the major problems.

Consider dies, for example: In a meeting between the die correctors, production control, press operators, and production supervisors, document the reasons for pulling dies before completion of the production lot. When all agree to the list, consult the engineering and maintenance persons. Problems which can be attributed to engineering and maintenance, such as die temperature variations and container and billet temperature variations, must be fixed as soon as possible.

Here are typical conclusions from such meetings:

• Dies must be managed into and out of die ovens.

• Die maintenance practices must be defined.

• Question and limit cleaning and polishing (an alternative is to leave metal in the dies).

• There must be practices stating the number of times a die goes to the press between cleaning and re-nitriding.

• There must be a standard for re-nitriding.

• The maximum number of billets before the die is removed from the press must be defined.

• The target life of each die must be defined.

• Operating practices.

• The maximum time in the die oven must be defined.

• Die maintenance practices must follow the AEC handbook.

Get everything right the first time, because lead time is the integrated measure of manufacturing performance!

(1) Baer, Austin R. “What’s in the Box?” Proceedings of the Fourth International Extrusion Technology Seminar, Chicago, IL, April 11-14, 1988, Volume II, 457-460

Waste - Part 4