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Visual Vs Mechanical Metal Inspection: The Pros and Cons of Each

Inspecting metal during the manufacturing and processing is crucial because there are plenty of opportunities for mix-ups

Thursday January 31, 2019 11:45 PM, Zohair M Safwan, ummid.com

Metal testing

Understanding the basics of metal inspection will help you to decide which one is right for your needs at the time. Metal inspection involves utilizing certain methods to determine whether there are flaws or not in the material.

Sometimes these methods themselves can be destructive, but if visual and mechanical methods of inspection are considered to be nondestructive. However, no method is 100% accurate and the one you need will depend on your intent for the inspection.

Inspecting metal during the manufacturing and processing is crucial because there are plenty of opportunities for mix-ups. In addition to accidental mistakes, counterfeiting of metals is on the rise since the scrap metal trade has become so lucrative. When metal is misidentified, it can come back on you, even if the initial mistake wasn’t on your end.

The fact is, it’s up to you to make sure that when the metal leaves your hands, it’s identified thoroughly and correctly. To do that, you need to choose between visual or mechanical inspection as your primary method used, and you need to understand the pros and cons of both.

Why is Metal Inspection Necessary?

Metal manufacturing is an integral part of millions of products. Other manufacturers rely on the integrity of the materials they purchase to be quality enough that their own products look good and do what they are intended to do. When metal is not inspected correctly or thoroughly enough, this deficient metal creates a domino effect of problems.

Metal inspection can happen any time during the production process. It’s commonly performed when the material is received, during designated stop points in production, or at the end of the entire manufacturing process before the product is sent for delivery. Occasionally, it happens during all of these steps. If a defect is discovered randomly, an inspection can be requested as well.

What is Visual Inspection?

Visual inspection helps you to detect multiple surface flaws. These may include such things as corrosion, surface finishes, and contamination, as well as other flaws. It’s the most common method used because it tends to be the easiest. However, it isn’t the most in-depth type of inspection.

Visual inspections can quickly let you know if there are any surface cracks that may cause structural failures. There is no potential for destruction with this type of inspection, and if you integrate equipment like inference microscopes to the exam done by the naked eye, you can get a pretty thorough analysis of the metal’s surface. Sometimes this is all that is needed for a good inspection, but sometimes the problems lay beneath the surface.

What is Mechanical Metal Inspection?

Metal inspection can be further clarified through a process called “mechanical metal inspection,” which simply means that the manufacturer analyzing the metal uses machines to automate the inspection process as much as possible.

This can include processes like Eddy Current Testing (ECT), in which electromagnetic induction is used to check for flaws like corrosion, pitting, and cracks. It also measures the thickness of the metal at specific areas.

However, mechanical metal inspection also involves human involvement, which means it’s not 100% accurate, either.

What are the Pros and Cons of Visual and Mechanical Inspection?

Whether you use high-tech machinery or visual tools to inspect your metal, there are going to be pros and cons to the way you choose. Some methods work better for one thing than another. What you need will depend on why you are inspecting the metal in the first place and what you are applying it to.

Visual inspection is the tried and true origin of all metal verification processes. It has been around for millennia and is still the go-to fallback method for all inspection processes. If you know what you are looking for, visual inspection is the most powerful method you can use. But there are weaknesses to this method over and above the capacity for human error.

No matter what manufacturing application you use, a visual inspection should be part of your process at some point. It has a lot of strengths, and there are reasons it has been an integral part of manufacturing for so long.

Visual inspection pros include:

  1. Obvious flaws can be found quickly, saving time and money that would otherwise have been spent in the inspection process on a piece of material that didn’t need to make it past the first inspection point.
  2. Visual inspection eliminates the possibility of overlooking errors in dimension and overall workmanship not evaluated in mechanical inspections.
  3. It’s a commonly used, relatively inexpensive, and easily replicated part of the inspection process.

But even with these pros, there are cons to visual inspection.

  1. The human eye is unreliable and can be tricked. Fatigue and other bodily processes can cause the eye to see things incorrectly or miss errors.
  2. Miniscule errors may be overlooked. The human eye can’t measure things to exact standards, so if an error is not easily seen by the naked eye, it may be overlooked. This applies to traits of metal such as size, texture, depth, and other measurable aspects.

Mechanical inspecting comes with a set of pros and cons, too. This type of inspection is good for:

  1. Obtaining unbiased information, such as size discrepancies and errors in dimensions.
  2. Analyzing unfamiliar metals.
  3. Times when accuracy is key.

Yet, mechanical inspections are not 100% reliable, either, and should always be used in conjunction with another method of inspecting because:

  1. There’s still a human factor involved and therefore human error is possible. People must program the machines and create accurate lighting, feed the parts into the machines, and direct pressure as necessary.
  2. Computers work sequentially rather than holistically, so all characteristics of the metal are not always analyzed.
  3. Putting metal through the system quickly is the most cost-effective, but least thorough, a method in regards to resolution and overall inspection.

Visual Vs Mechanical - Which Method is Best for You?

Each inspection process, no matter which one you choose, should always be followed by a method of verification because none of them is 100% accurate. However, the application you use will determine whether you need a predominantly visual inspection with a mechanical back-up, or whether you can save time and use a mostly mechanical inspection with a visual follow-up.

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