Is Your Scrap Rate Increasing? 5 Common Causes and Tips to Address It

If you discover your scrap rate is creeping up, you’re probably having these two thoughts at once: What’s the cause? and How can I eliminate the cause quickly?

We’ve seen teams burn weeks chasing the wrong “obvious” cause because they “didn’t have time” to organize a clean approach to narrow it down and ended up spending more time unproductively. So we wrote this article to hopefully save you that time and provide takeaways to consider, including:

• What is “high scrap?”
• A quick way to tell “one bad day” from a real trend
• The five most common scrap drivers we see on manufacturing lines
• Some practical tools that work without slowing production

What Is Scrap Rate?

Scrap rate measures the percentage of material or parts discarded for not meeting spec. It’s a KPI that tracks how much of what you make ends up as waste instead of a shippable product.

How to Calculate Scrap Rate

Scrap rate equals scrapped units divided by total units started or produced. The exact definition should match how your team tracks production.

A simple version: Scrap Rate (%) = (Scrapped Units ÷ Total Units Produced) × 100

Two quick thoughts for setting up your calculation:

• Decide whether rework counts separately. It’s most common to track scrap and rework separately because rework still eats time and cost, but it doesn’t always result with product in the dumpster.
• Be consistent with the denominator. Switching between “units started” and “units produced” makes trends and comparison messy.

Ultimately, the most important thing is that you are measuring scrap and secondly that you track it at an appropriate level of detail to provide the information you need to address it.

What’s a “High” Scrap Rate Benchmark?

We’re careful with suggesting what’s a “normal” benchmark because scrap rate thresholds vary depending on your product, process, and industry risks.

Instead of chasing a universal number, we recommend you answer two questions:

1. Is our scrap rate trending up month-over-month or shift-over-shift?
2. Is scrap hitting our bottleneck step or our most expensive material(s)?

Those two signals matter more than any generic benchmark. And if you still want a scrap rate reaction threshold, it should be set based on your particular business case and prioritization of your available resources.

Why Is My Scrap Rate Increasing?

Scrap spikes come from changes in inputs like materials, machines, methods, environment, or people. When scrap rises suddenly, something changed in one or more of those inputs and finding a special cause within is key to improvement. Alternatively, scrap rates may rise gradually, trending in an objectionable direction which may require different techniques to reach the root cause.

The Difference Between a One-time Spike vs. a Real Trend

A spike indicates a single event; a trend indicates a system shift. Here’s how we can tell that difference quickly:

• A spike usually ties to an abrupt change to one or more inputs. Look for scrap increase associated to one lot, one shift, one machine, one setup, one new operator, or one tooling event.
• A trend usually ties to drift in one or more inputs: wear, calibration, documentation gaps, training gaps, or design changes piling up are some examples.

Again, you need to decide the appropriate level of detail your team records with scrap. If your scrap data is vague (e.g., “bad part” or “defect”), you’ll most likely stay stuck. So, make sure you have the “where” and “what” before you ask “Why?”

The 5 Most Common Reasons Scrap Rates Increase

Rising scrap signals sudden or gradual change in manufacturing inputs. Below are the five causes we run into most:

1. Poor or inconsistent raw material quality
2. Equipment wear, calibration issues, or deferred maintenance
3. Process method variability and lack of standardized work
4. Gaps in operator training or high workforce turnover
5. Design or engineering decisions that don’t account for manufacturability

1. Poor or Inconsistent Raw Material Quality

Material quality drives defect rates and process stability. When material is too inconsistent, it will be evident in your scrap rate.

What material-related scrap looks like on the line

You’ll often see:

• Defects clustered around a certain lot
• Scrap that shows up early in the process
• Operators saying “this material feels different” (they’re often right)

Common supplier/material causes

Material problems aren’t only due to “bad” suppliers. We also see issues from:

• Lot-to-lot variation that’s still “within spec,” but not stable enough for your process
• Improper storage (moisture, temperature, contamination)

How to explore material as the root cause

Some quick checks are:

• Compare scrap by lot number
• Check incoming material certification or inspection report trends (even basic measurements)
• Run a short trial with a known-good lot if you have one and see if you can turn the problem off and then on by switching between lots

What to do if material quality is driving scrap

Containment first:

• Hold suspect lots
• Add temporary checks at receiving or first operation
• Engage the supplier

Prevention next:

• Tighten supplier feedback loop with evidence
• Update quality systems based on what failed, not just what’s easy to measure
• Review process interactions with material and optimize

2. Equipment Wear, Calibration Issues, or Deferred Maintenance

Equipment condition affects dimensional accuracy and repeatability. Small machine drift becomes big scrap when it runs for days.

How worn components and “almost-right” calibration create scrap

This is one of the most expensive traps: the machine still runs, parts still come out, but capability is fading. Scrap can climb quietly until someone notices the bin.

Warning signs maintenance teams often see before the scrap spikes

• More frequent minor adjustments by operators
• Longer or more difficult setups
• More “tweaking” to hit numbers
• Scrap that follows one machine or fixture

What to check first

We start with:

• Interview operators for insights
• Tooling wear and fixture play
• Condition and function of machine instrumentation
• Process setups that rely on “feel” instead of a measurable setting

Short-term fixes vs. long-term maintenance improvements

In the short term, you can re-calibrate, swap tooling, and/or lock critical settings. In the long term, you could build a maintenance trigger tied to quality drift, not just time.

3. Process Variability and Lack of Standardized Work

Process variability increases defect opportunity across shifts and setups. Even good people can make inconsistent parts when the method is inconsistent.

How small variations compound into big scrap numbers

A half-turn on a knob. A different way to seat a part. A shortcut during setup. One person’s “close enough.” These stack up fast!

Where variability usually hides

Some common hiding spots are:

• Set up or run sheets that aren’t accurate
• Tribal knowledge steps that live in one person’s head
• Shift handoffs where problems aren’t clearly passed forward

What to look for in work instructions and documentation

• Steps written as “verify correct setting” without telling what “correct” is
• Missing photos, go/no-go examples, or reject examples
• No clear stop-the-line rule

How to stabilize the process without slowing production

Start small. Try one or more of these items:

• Standardize the top 1-2 setups that generate the most scrap
• Add visual controls at the point of adjustment
• Make “scrap tagging by operation” non-negotiable for a short window

4. Gaps in Operator Training or High Workforce Turnover

Training gaps show up as repeatable scrap patterns tied to people and shifts. We don’t like blaming operators because we’ve found that when scrap is tied to people, it’s most often a support and/or system issue.

How training issues show up in scrap patterns

Look for:

• Scrap spikes on certain shifts
• Scrap linked to certain stations with frequent staffing changes
• High scrap right after onboarding waves

Why “operator error” is often a systems problem (not a people problem)

If the work requires judgment, you need:

• Clear boundaries (what’s acceptable, what’s not)
• Fast escalation when something seems off
• Tools that make the right action easy

What to validate

• Who is certified for each operation
• Is the use of administrative controls and poka yokes optimized?
• Tools that make the right action easy

Practical ways to reduce scrap through better support and training

Here are some quick wins you can implement right away:

• Add a 10-minute daily quality huddle at the top scrap operation
• Create a short “top 5 defects” visual guide at the station
• Pair new operators with one consistent trainer for the first week

5. Design or Engineering Decisions That Don’t Account for Manufacturability

Design decisions influence scrap by setting tolerance and process difficulty. A part can be “designed right” and still be painful to build.

How design tolerances and feature choices create scrap downstream

Some examples we’ve seen:

• Tight tolerances in places that don’t impact function
• Features that require delicate handling or hard-to-control steps
• Stack-ups that are fine on paper but unstable in real life

When ECOs/ECNs and spec changes increase scrap unintentionally

Engineering change orders can raise scrap when:

• Documentation isn’t synced
• Old stock is still in circulation
• Inspection plans aren’t updated

How to spot DFM-related scrap (and what evidence to gather)

• Scrap photos by defect type
• Measurement data showing where variation occurs
• Notes from operators about what’s hard to hold consistently

How to Find the Root Cause of Scrap (Without Guessing)

Root causes analysis connects scrap symptoms to a verified cause. While guessing can feel fast, it usually ends up wasting time.

The simple root cause workflow we use is define, contain, identify, confirm, prevent.

1. Define: Clearly and accurately define the problem statement.
2. Contain: Stop the bleeding. Segregate, add checks, and/or protect shipments.
3. Identify: Use a systematic approach to identify a root cause.
4. Confirm: Prove the cause with a test. This could include swapping the material lot, recalibrating, or running a controlled setup.
5. Prevent: Update the system with standardized work, maintenance triggers, supplier checks, operator training, and/or design for manufacturability (DFM) guidelines.

Tools You Can Use

Some basic tools to use are communication, Pareto analysis, OEE tracking, and adopting a cost of quality mindset.

• Excellent communication, including an open mind and listening skills, are key to addressing issues and developing the best permanent solutions.
• Pareto is an analysis tool that can help you find the biggest defect categories first.
• OEE and first pass yield measurements can help you track how many parts pass without rework.
• Adopting a cost of quality mindset will help you and your team see the bigger picture on how much scrap and rework are actually costing and why it’s important to keep an eye on them.

When It’s Time to Bring in Outside Manufacturing Support

Sometimes scrap issues have causes that are complex or due to input interactions, and you may need fresh eyes and more specialized approaches.   Furthermore, outside help can be useful when you need a neutral party to align cross-functional challenges among engineering, quality, ops, and suppliers quickly.

If you want help with reducing scrap rate in your plant, our team can help. We can help you identify the problem and create the solution for it. Contact us here to get started.