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What Is Sheet Metal Hemming and Why It Matters

What Is Sheet Metal Hemming and Why It Matters

 

In custom sheet metal work, the edge is everything. A razor-sharp edge on a kiosk can slice a nurse’s hand or a child’s finger in seconds. A flimsy door edge on an outdoor cabinet warps the first time someone leans on it. On the other hand, a properly folded and crushed edge turns a plain panel into something strong, safe, and honestly good-looking. That fold is called a hem, and once you see how much difference it makes, you’ll never look at a metal box the same way again.

We are San Jun Hardware, a factory that’s been running since 2010. We cut, bend, weld, and finish custom sheet metal parts for customers all over the world. You’ll find our work in hospitals, fast-food restaurants, roadside digital signs, vending machines, and classroom podiums. When the job calls for safe, stiff edges that last, hemming is one of the first things we reach for.

The Necessity of Edge Reinforcement and Safety

Right after the laser or punch cuts a blank, every edge is sharp enough to draw blood and weak enough to bend if you grab it wrong. Leaving it that way is asking for trouble.

Achieving Structural Rigidity and Durability

Fold the edge back on itself, and you double the thickness right at the place that normally flops around the most. A 1.5 mm cold-rolled steel panel with a 180° closed hem acts like it’s 3 mm thick along that side. Doors stop rattling, lids don’t oil-can, and the whole box feels solid when you pick it up.

In medical carts and pharmacy dispensers we build, the cleaning crews bang those doors open and closed hundreds of times a day. A hemmed edge is the difference between a cabinet that stays straight for ten years and one that looks beat-up in six months.

Ensuring Safety in Public Spaces

Nobody wants a lawsuit because someone cut their hand on your kiosk. Hospital Self-Service Kiosk Enclosures sit at perfect kid-height, so every outside corner gets either a full closed hem or a generous radius return. The same goes for Intelligent Self-service Cabinets in train stations—drunk passengers lean on them, kids climb them, and the edges still have to stay smooth and safe.

 

The Sheet Metal Hemming Process and Types

Hemming isn’t just “bend it over.” It’s usually a careful two-step dance so the metal doesn’t crack or bulge.

The Two-Step Folding Mechanism

  • Pre-bend – We take the edge up to about 135–140° on an AMADA CNC press brake. This step lets the material relax a bit before the final crush.
  • Flatten – A special hemming die (or a simple flat tool on the brake) smashes the flap the rest of the way down until it’s dead flat against the panel. Done right, you can barely feel where the edge stops.

Variations in Edge Finishing

  • Closed Hem – Completely flattened, zero gap. Stiffest and safest. We use this on every door edge that faces the public.
  • Open Hem (sometimes called teardrop or roped hem) – Leaves a small, round tube-like edge with a tiny gap inside. Looks nice on appliance panels and gives a comfortable grip, but it isn’t quite as rigid as a closed hem.

Applications in San Jun Hardware’s Specialized Enclosures

Securing Outdoor Infrastructure

Outdoor boxes take a beating from weather and people. Outdoor Custom Digital Signage Shell IP65 units sit on sidewalks in blazing sun and freezing rain. The doors on these cabinets are 2 mm aluminum with closed hems top and bottom—water can’t sneak in, and the edge won’t peel open after a few seasons. The same heavy hems go on the IP65 Self-service Terminal Integrated Machine Shell you see at gas stations and bus stops.

 

Touch Display Advertise Enclosure

Integrating Aesthetics and Security in Display and Vending

Walk up to any 24″, 27″, or 32″ Self-service Ordering Kiosk in a burger joint and run your hand along the side. You won’t find a sharp edge anywhere because every visible flange is either hemmed flat or rolled. The same treatment shows up on Custom Automatic Distributor Vending Machines—the doors are thick enough to stop a crowbar, yet the edges feel rounded and friendly.

Precision Processes Supporting Hemming Goals

Material Foundation and Cutting Precision

Everything starts with clean material and clean cuts. We stock cold-rolled steel, galvanized, 304/316 stainless, and several aluminum alloys. The laser cutters (3000 W fiber machines) hold ±0.1 mm on material from 0.5 mm to 2.0 mm thick, so when we fold that hem later, the flap is exactly the right length—no short hems, no bulges.

Shaping and Joining for Strength

After cutting, parts move to the AMADA CNC press brakes for the pre-bend and final flattening. Welders then tie multiple panels together with MIG, TIG, or spot welds, depending on material and appearance requirements. The whole line runs under our ISO9001:2008 system, so every hem gets checked with a go/no-go gauge before the part leaves the floor.

Surface Finishing for Longevity

A good hem is strong, but powder coat or passivation makes it last. Outdoor pieces get 80–120 μm of UV-stable powder, so the folded edge stays pretty after years of sun. Stainless medical boxes get glass-bead blasted and passivated—the hem stays shiny and germ-free shift after shift.

Conclusion: Custom Fabrication Driven by Detail

A hem is only a couple of millimeters of folded metal, but it changes everything: stiffness, safety, looks, and how long the product survives in the real world. At San Jun Hardware, we’ve got the brakes, dies, and people who do this all day, every day. Send us a drawing that calls for safe edges, and we’ll pick the right material, cut it clean, hem it tight, weld it strong, and powder-coat it tough, and ship boxes you can be proud of. No hard tooling charges, samples in 3–7 working days, and the same quality from the first piece to the ten-thousandth.

FAQ

Q: What are the main advantages of San Jun Hardware’s custom sheet metal fabrication services?

A: Safe, rounded edges, stronger panels, better looks, and parts that last longer—plus fast quotes and no expensive die costs.

Q: What precision level can San Jun Hardware guarantee for sheet metal cutting?

A: ±0.1 mm on our 3000 W laser cutters for material 0.5 mm to 2.0 mm thick.

Q: What guarantees the durability of the Outdoor Custom Digital Signage Shell IP65?

A: Heavy material, closed hems, fully sealed welds, proper gaskets, and thick UV-resistant powder coat that delivers real IP65/IP66 protection and IK10 impact rating.

Q: How quickly can San Jun Hardware provide a sample for a custom part?

A: 3–7 working days after we agree on the price and you sign off on the drawings.

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FAQ

We usually quote within 24 hours after we get your inquiry. If you are very urgent, pls call us or tell us in your email so that we will regard your inquiry priority.
After price confirmation, you can require for samples to check our quality. We will provide you sample for free (value under USD15), as long as you afford the express freight.
After you pay the sample charges(if there is) and send us confirmed drawings, the sample will be ready for delivery in 3-7 working days. The samples will be sent to you via DHL, FedEx,UPS,TNT or EMS. It should arrive in 3-5 workdays. You can use your own express account or prepay us if you don't have any account.
Honestly, it depends on the order quantity. Normally, 15 days to 20 days after your deposit if no tooling needed.
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