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A phone case that looks perfect can still fail the moment it hits the ground.
For brands developing protective cases, drop test failures are among the most frustrating problems during product development. They often appear late in the project, delay production schedules, increase tooling costs, and reduce confidence in the final product.
Many people assume the material is the only reason a case cracks.
In reality, impact performance depends on a combination of engineering decisions made long before mass production begins.
Here are seven factors every product manager and sourcing team should understand.
1.Material Selection Matters More Than Most People Think
Different grades of PC, TPU, TPE ,and PC/TPU/TPE combinations behave differently under impact.
Choosing a resin simply because it is specified on the drawing is rarely enough.
Engineers should evaluate:
• Impact strength
• Melt flow rate
• Thickness suitability
• Long-term durability
Material selection should always match the product’s structural design and expected use conditions.
2.Part Thickness Is a Structural Decision
Even high-performance materials can crack if wall thickness is not optimized.
Thin walls may reduce weight but also reduce energy absorption.
The goal isn’t making the case thinner.
It’s finding the balance between protection, appearance, and manufacturability.
3.Mold Design Influences Mechanical Performance
Gate location.
Runner balance.
Cooling channels.
Vent design.
All influence how internal stress forms during injection molding.
A visually perfect part may still contain residual stress that weakens impact resistance.
4. Injection Molding Parameters Affect Internal Stress
Stable molding conditions are just as important as good tooling.
Variables such as melt temperature, mold temperature, holding pressure, and cooling time all affect the final mechanical properties.
Consistency is often more valuable than chasing the fastest cycle time.
5. Assembly Can Change Performance
Many protective cases include additional processes:
Leather wrapping
Printing
Lamination
MagSafe assembly
Adhesive bonding
Each process introduces new stresses that should be validated as part of the finished product—not only on individual plastic components.
6. Laboratory Testing Should Simulate Real Use
Testing only one sample is not enough.
Good engineering validation includes:
Different drop heights
Multiple impact angles
Conditioned samples
Repeated testing
Complete assembled products
The objective is to evaluate repeatability rather than a single successful result.
7. Engineering Collaboration Reduces Risk
Many failures originate from communication gaps rather than manufacturing defects.
The best projects involve design, tooling, molding, quality, and sourcing teams early in development.
Problems identified before tooling are significantly less expensive than problems discovered after mass production begins.
Conclusion
A cracked phone case is rarely caused by one single factor.
Material, tooling, molding, assembly, and validation all contribute to the final performance.
Brands that understand these engineering relationships can reduce development risk, shorten project timelines, and improve product reliability.
At Sendtin, we believe successful products are built through engineering collaboration—not trial and error.
Planning a new protective case project?
Our engineering team supports brands from DFM review and material selection to tooling, injection molding, testing, and mass production.
Feel free to contact us to discuss your next OEM or ODM project.
