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Machine Scrap
Machine scrap is an informal term used to describe any wasted material that is produced when machining, including material that is removed, and whole parts that do not meet specifications and are not repairable. The term "scrap" can also be used as a verb to describe what to do with a part when it is determined that the part does not meet specifications. The use of this term for this article does not include "scrapping" a machine itself, which is revenue which is used to perform life cycle analysis on a machine or system.

Difference Between Rework and Scrap
Machine scrap does not include parts that may be able to be reworked into specs. For instance, if a hole is supposed to be ø 1mm, but it is only ø .5mm, it can be reworked by using a larger cutting tool to create a hole that is the correct size. While this is a waste of time and money, the part is not considered scrap. Rework can be done by repeating the process or moving forward with a repair process.

In the instance where a hole is supposed to be ø 1mm, a ø 1.5mm hole would make the part scrap if it is not economically feasible to repair it. When a part is scrapped, it may be discarded or recycled. Recycling a product may recover some of the lost revenue, but will be a loss to the manufacturer.

Causes of Scrap in Machining
Sometimes a machine crash, which is unplanned contact between a machine and a part being machined, can cause scrap.

Alternately, if a product is sent to the next stage in production with a defect, it could cause a machine crash. For example, if a hole is supposed to be ø 5mm before being bored to 5.05mm, but the hole arrives at the operation at ø 2 mm, the boring bar would very likely be broken when it tries to bore out the hole.

In many industries, such as subtractive manufacturing, scrap is an inevitability due to the nature of the machining processes which remove material from the part being machined.

Cost of Scrap
While machine scrap is inevitable in some industries, it is beneficial for companies to reduce the amount of scrap that is created during the material removal process because the reduction will reduce operating costs by extending tool life while lowering the time and effort required to create a part that meets specifications.

There are hidden costs when unexpected scrap is encountered. For the manufacturer, time and money are lost. The manufacturer may have downtime, machine wear, remedial training, and a host of other costs as the result of machine crashes. Under certain circumstances, the manufacturer may not be able to fulfill an order from a customer, which damages the manufacturer's reputation, but the reputation of a company will suffer more if the scrap parts are released to the customer. "Contamination" occurs when scrap parts or parts that need rework become mixed with good parts.

When a customer receives faulty parts from a manufacturer, the process required to remove the bad material from circulation becomes much harder to facilitate if the mistake is not caught early. In manufacturing, the cost of scrap material increases as more time is invested into making the part closer to a finished product, as the material becomes more expensive, and as size of the parts increase, as a larger scrapped part will often result in more lost money. Much of manufacturing is creating components which will be used as part of an assembly. If a part is bad on an assembly, then the entire assembly may need to be disassembled to remove the faulty part. This is very costly, and examples of this happening are easy to find in the automotive field, in which "recalls" to remove faulty materials are published to reduce the chance of injuries or death to consumers. If faulty products cause serious harm or death, then along with the cost to repair the mistake in all of the affected parts, the companies involved in manufacture may incur heavy legal costs due to resulting lawsuits.

Preventing Scrap
Preventing scrap is the most cost-efficient path to take in most cases. To prevent scrap, a good quality management system needs to be in place. A good quality management system will institute checks to ensure part compliance along every step of the way. Quality management systems also focus on training employees to be proficient at their job, and to recognize issues that may compromise quality. A good quality program also takes steps to prevent events that would harm quality, such as preventing the risk of damage that could be caused while manually handling delicate parts by minimizing the instances an employee has to move the part by hand.

Subtractive manufacturing's inevitable scrap can be reduced by specifying smaller castings, when possible, from which the parts are produced.