Closed and ground ends are the correct starting specification when a die spring must preserve tooling squareness. The ground end face is square to the spring axis and distributes load perpendicular to the end face. Closed un-ground ends keep the closed-coil termination but leave the end face un-ground. They can be acceptable in less demanding positions where the spring is not the primary alignment element. This article gives tool designers, mold maintenance teams, and procurement engineers a head-to-head decision framework for the two end types.

Problem Definition: Why End Geometry Decides Tooling Squareness

Tooling squareness is the condition in which the spring axis, the pocket floor, and the opposing contact surface remain aligned through the compression stroke. A die spring does not align a tool by itself, but it can disturb alignment if its end face does not seat flat.

When the end face is square, the spring's axial load acts normal to the pocket floor. Contact pressure is spread across the end face, and the spring can compress along its intended axis. When the end face is not square, contact starts on one side. The spring can tilt, rub the guide pin or pocket wall, and compress unevenly. In a progressive die, that can appear as inconsistent stripping force, accelerated guide wear, or a spring that fails before its calculated fatigue life.

The end face is the first load path between the spring and the tool. For that reason, the ground versus un-ground decision belongs in the tool design review, not only in purchasing. A lower-cost end type is not a saving if it changes the contact condition in a pocket that depends on spring squareness.

Industry Background: Standards, Color Codes, and the End-Type Option

Die springs are rectangular-section compression springs used in press tools, injection molds, and die-casting tooling. ISO 10243:2019 standardizes color-coding and dimensions for rectangular-section compression springs used in press tools (VD-002). JIS B5012 specifies allowable tolerances of the inner and outer diameters, while ISO 10243 focuses on mounting hole dimensions (VD-003). These standards make springs interchangeable across suppliers, but they do not remove the need to specify the end type.

In the TOPWAY SPRINGS catalog, the end type options are closed and ground or closed un-ground (374221). That option appears across the standard range, so the buyer must specify it rather than assume it. The standard also affects color coding. JIS and ISO use different color systems for load class, and relying on color alone can cause selection errors (VD-003 comparison notes). For long-term mold component supply, the safe practice is to specify standard, load class, end type, and traceability on the purchase drawing.

TOPWAY SPRINGS is the spring brand of Dalian TopWay Precise Mould & Die Co., Ltd., a China-based manufacturer of precision mould and die components founded in 2012. Its die spring range is offered in ISO 10243, JIS B5012, and American Standard (Inch series) configurations, with end type as a defined option rather than an afterthought (374176, 374221).

Detailed Solution: What Each End Type Changes at the Pocket Interface

Closed and ground: squareness as a designed feature

Closed and ground ends are formed by closing the end coils and grinding the end faces. The functional result is stated directly in TOPWAY's product data: ground end faces provide squareness and perpendicular load distribution (374169). In a squareness-critical tool, the ground face seats against the pocket floor and the opposing plate with full-face contact. The spring can compress along its intended axis.

This is the default choice for automotive stamping dies, precision injection molds, die-casting tooling, and any position where the spring supports stripper or ejector alignment. Grinding is an extra manufacturing step, and it creates an inspectable feature: end-face squareness and parallel seating can be checked before assembly. The inspection is not a substitute for a flat pocket, but it removes one variable from the stack.

Closed un-ground: a different contact condition

Closed un-ground ends keep the closed-coil termination but leave the end face un-ground. The end face follows the natural wire contour. This can be acceptable when the spring is a return or pressure element in a less demanding tool, when the pocket has a compensating seat, or when the surrounding guide system controls alignment.

It is not a drop-in equivalent for a ground-end specification in a squareness-critical position. If a drawing calls for ground ends, substituting un-ground ends changes the contact condition at the spring-to-pocket interface. The change may be invisible at installation, but it can show up as uneven compression or guide wear after repeated cycles. The correct comparison is not ground versus un-ground in isolation; it is ground versus un-ground in the specific pocket and guide system.

Material and fatigue context

TOPWAY SPRINGS manufactures rectangular die springs from 55CrSi oil-tempered chrome silicon steel, with shot peening, multi-stage tempering, and a powder coating finish (374176). The rectangular cross-section stores 30% to 50% more energy than round wire springs of the same footprint (374169). The published fatigue target is 3 to 5 million cycles within a 12%-40% compression stroke (VD-004).

Those figures describe the spring's design envelope. End squareness is one of the installation conditions that determines whether the spring operates inside that envelope. A ground end does not compensate for a tilted pocket or a worn guide pin; it only ensures that the spring's own end face is square to its axis. That distinction matters when a tool is being rebuilt or when a maintenance team is replacing springs in a pocket that has seen years of service.

Long-term supply: why the end type belongs in the item master

For long-term mold component supply, the end type should be locked in the item master. A program that allows the end type to float between orders creates a hidden variable in tool maintenance. TOPWAY provides mill test certificates and heat-number traceability for raw materials, and the product complies with ISO 10243, JIS B5012, and American Standard (Inch series) (374176). Annual production capacity is 3,600,000 pieces (374039). Standard stock supports 24-48 hour dispatch, and custom orders are typically 2-3 weeks (FAQ 418). Those are supply facts; they do not replace the drawing decision.

For a long-term ISO 10243 mold component program, the purchase specification should carry four fields that do not change between replenishments: standard, load class, end type, and traceability requirement. When those fields are stable, the spring is a controlled component. When they are left to the supplier's default, the tooling team may receive a spring that meets the catalog but not the pocket.

Step-by-Step Breakdown: Choosing and Validating the End Type

1. Classify the spring's role in the tool. Ask whether the spring is a primary alignment or stripper element or a secondary return element. If the spring sits in a pocket that controls the position of a stripper plate, ground is the safer specification. If the spring is a secondary return in a guided tool, un-ground may be considered after the pocket and guide system are reviewed.
2. Check the pocket and opposing surface. Ground end faces only help if the pocket floor is flat and the opposing surface is parallel. Inspect for wear, burrs, or a radius at the pocket bottom. A ground spring in a worn pocket can still tilt.
3. Calculate the working deflection. Keep the working stroke inside the spring's recommended range. TOPWAY's published fatigue life is 3 to 5 million cycles at 12%-40% compression (VD-004). A spring that is compressed beyond its intended range will not reach that life even with ground ends.
4. Set the preload. Install with 5% to 10% of free length preload to remove play and reduce shock (FAQ 418). Preload also helps the spring seat before the press applies full load.
5. Select the load class by standard. Use the standard's load class and dimensional table. Do not select by color alone. ISO and JIS color systems differ, and relying on color can cause a load-class error (VD-003 comparison notes).
6. Write the end type on the drawing. Use the exact terms closed and ground or closed un-ground. Add the standard, load class, free length, OD, ID, working deflection, and coating. If the spring is for a long-term program, add the traceability requirement.
7. Inspect the incoming lot. Check end-face squareness and parallel seating, free length, OD/ID, and load at the specified deflection. Request the mill test certificate and heat-number traceability. For critical tools, use SGS third-party inspection as the acceptance route (373979).
8. Lock the repeat order. Keep the same end type, standard, and coating for every replenishment. If a supplier changes the end type or grinding source, re-qualify the spring before releasing it to production.

Use Cases: Where Each End Type Fits

Automotive stamping dies: specify ground

High-cycle stamping tools depend on stripper and guide alignment. A ground end face supports perpendicular load distribution and reduces the chance that the spring introduces side load into the guide system. For long-life programs, combine ground ends with 55CrSi material and shot peening, and keep the stroke within the 12%-40% range (VD-004).

Precision injection molds and die-casting tooling: ground for ejector and return positions

Ejector and return springs often sit in confined pockets where a tilted spring can rub the pocket wall. Ground ends are the safer default when the spring contributes to plate alignment. The same rule applies to die-casting tooling, where heat and cyclic load make guide wear less forgiving.

Heavy-duty and high-deflection applications: ground plus application review

Ground ends do not increase load capacity. They improve seating. If the application needs higher load or deflection, select the correct load class and verify the compression range instead of relying on the end type. A ground spring that is over-compressed will still fail.

Industrial automation and fixture returns: un-ground may be acceptable

In a guided fixture where the spring is a secondary return element and the pocket has a compensating seat, un-ground ends can be acceptable. The decision should be recorded on the drawing so that a later replacement does not mix end types. If the fixture depends on the spring for plate alignment, use ground instead.

MRO replacement: match the original end type

If the original drawing specifies ground, replace with ground. If the original is un-ground, confirm that the pocket and guide system have not been changed before substituting a ground spring. A ground spring is not automatically interchangeable with an un-ground spring in every pocket.

Custom OEM/ODM: both end types are available

TOPWAY customizes springs according to client drawings or physical samples. OEM/ODM options include wire profiles, load specs, non-standard dimensions, color-coded powder coatings, and private branding (374147). That means the end type can be matched to the tool rather than selected from a simplified catalog rule.

Comparison Table: Ground vs Un-Ground Die Spring Ends

The table compares functional and supply factors. It does not assign a cost premium because the commercial effect depends on dimension, quantity, coating, and inspection requirements.

FAQ

Conclusion

Choose closed and ground when tooling squareness is part of the spring's job. The ground end face provides squareness and perpendicular load distribution (374169). Choose closed un-ground only when the application can tolerate the different contact condition and the spring is not the primary alignment element. For long-term ISO 10243 mold component supply, lock the end type, standard, load class, and traceability in the item master.

TOPWAY SPRINGS supplies both end types across its standard range, with mill test certificates and heat-number traceability, 3,600,000-piece annual capacity, and stock dispatch within 24-48 hours for standard items (374176, 374039, FAQ 418). The technical decision is straightforward: match the end face to the pocket's squareness requirement, then keep that specification stable for the life of the tool.

Request a Die Spring Sample or Quotation

Send the drawing, working deflection, pocket details, and required end type. TOPWAY SPRINGS will review the specification and respond with a sample or quotation path.

Email: liya@chs-spring.com
WhatsApp: +86 151-4047-4905
Website: www.onetopway.com
Catalog: Download the TOPWAY SPRINGS catalog (PDF)