Fuse Cap

 

Copper outer caps and brass inner caps serve different functions within fuse assemblies. Material selection affects electrical conductivity, forming behavior, dimensional stability, and the compatibility of mating components. A suitable specification must account for both the finished cap geometry and the conditions under which the fuse operates.

Copper Outer Caps for Conductive Fuse Terminals
T2Y2/C1100 copper is used in applications where high electrical conductivity and thermal conduction are required. Apollo's published material specifications identify T2Y2 red copper with conductivity of at least 97% IACS and a hardness range of HV 80–110 for applicable stamped components. The actual material condition should be verified against the product drawing and incoming material certificate.

Copper strip thickness, temper, and forming radii affect the finished cap's wall thickness, roundness, and resistance to cracking. Deep-drawn or multi-stage formed caps require controlled blank geometry, punch and die clearance, lubrication, and forming sequence. These factors influence the consistency of the cap's contact surface and its fit with the fuse tube or internal assembly.

Brass Inner Caps for Mechanical Fit
H65 brass is used for formed electrical components where a balance of strength, formability and conductivity is required. Its electrical conductivity is lower than that of high-purity copper, so the material should be selected according to the component's electrical role rather than substituted solely on the basis of mechanical strength.

For brass inner caps, the drawing should identify critical diameters, hole positions, formed height, wall thickness, and any mating or retention features. The tooling design should account for springback and material flow, particularly around perforations, flanges and drawn walls.

Precision Stamping and Tooling Control
Progressive die stamping is suitable for repeat production when component geometry and production volume justify dedicated tooling.

 

For more deeply formed caps, staged forming operations can distribute deformation and reduce the risk of wrinkles, tearing, or uneven wall thickness.

The manufacturing review should identify:
Material grade, temper and incoming thickness.
Critical dimensions and datum references.
Burr direction and edge-condition requirements.
Forming depth, corner radii and permissible wall-thickness variation.
Required inspection frequency and first-article acceptance criteria.
Annual demand, tooling ownership and revision-control requirements.

 

Fuse Cap Material and Manufacturing Specifications

 

Parameter	Copper outer cap	Brass inner cap	Inspection method
Typical material	T2Y2/C1100 copper	H65 brass, where specified	Material certificate
Electrical conductivity	Published material specification ≥97% IACS for applicable T2Y2 components	Grade- and temper-dependent	Conductivity test or certified material data
Hardness	HV 80–110 for the published T2Y2 specification	Defined by material grade and temper	Hardness test where required
Forming process	Stamping and drawing according to geometry	Stamping, drawing and perforation where required	First-article inspection
Critical dimensions	Diameter, height, wall thickness and mating fit	Diameter, perforation, flange, and mating fit	Optical measurement, gauges or CMM
Surface treatment	Tin, silver, or nickel plating where specified	Tin, silver, or nickel plating where specified	Coating specification and thickness measurement
Acceptance criteria	Customer drawing and approved control plan	Customer drawing and approved control plan	Inspection records and lot traceability

 

The values above apply only where the stated material grade and condition match the product. Final acceptance criteria must be agreed in the component drawing or quality plan.

 

 

A fuse cap's surface condition and joining interface affect assembly consistency, electrical contact and resistance to environmental degradation. Surface treatment should be selected according to the substrate material, mating component, service environment and customer specification.

Tin, Silver and Nickel Plating
Tin plating is used for many electrical terminal interfaces where the coating must provide a specified contact surface and corrosion performance. Silver plating may be selected for contact applications requiring appropriate electrical contact characteristics. Nickel plating can be used where a barrier layer or defined surface protection is required.

The coating specification should identify the plating system, minimum local thickness, measurement locations, and applicable acceptance criteria. The coating thickness must be verified rather than inferred from the appearance of the finished cap. For projects involving a specified 3–10 µm coating, the actual target and minimum thickness should be confirmed for the relevant material, geometry, and plating process.

Ultrasonic Cleaning and Surface Preparation
Stamped copper and brass components can retain forming lubricant, particles or residues that interfere with subsequent plating and joining. Ultrasonic cleaning can be used as part of the specified cleaning process before surface treatment or assembly.

The process should define the cleanliness requirement, rinse conditions, drying method and handling controls after cleaning. Where caps are supplied for subsequent welding, brazing or soldering, surface preparation must be compatible with the joining process and the permitted delay between cleaning and assembly.

Joining Methods for Cap Assemblies
Where the cap is supplied as part of a welded assembly, the joining process should be selected according to joint geometry and material compatibility. Resistance welding, tin soldering, and silver brazing may be suitable for different configurations. The process specification should define joint location, permissible distortion, electrical resistance criteria, and mechanical retention requirements.

Recommended process controls include:
Verification of plating thickness at specified locations.
Inspection for bare areas, blistering, scratches, and coating defects.
Prevention of contamination on finished contact surfaces.
Dimensional checks after forming and plating where coating build-up affects fit.
Electrical resistance and mechanical retention tests where required by the customer.
Batch identification linking material, forming, and surface-treatment records.

 

 

Incoming Material Verification
Incoming inspection should verify material grade, thickness, and condition against the approved drawing or purchase specification.

 

Material certificates should be traceable to the supplied lot. Where conductivity or hardness is a critical requirement, the inspection plan should define whether acceptance is based on certified material data, periodic testing, or lot-specific verification.
Dimensional Inspection

The inspection plan should focus on features that affect assembly:
Outer diameter and inner diameter.
Cap height and formed-wall profile.
Roundness, flatness, and perpendicularity where specified.
Wall thickness and local thinning for drawn components.
Perforation position, hole size and edge condition.
Mating fit between copper outer caps and brass inner caps.

Optical measurement systems, calibrated gauges and CMM equipment may be selected according to part size, geometry and required measurement uncertainty. A tolerance such as ±0.01 mm should be specified only for dimensions that the selected manufacturing process and measurement method can consistently support.

Surface and Assembly Verification
For plated components, inspection should cover coating type, thickness, and visible defects. For joined assemblies, the control plan may include visual inspection, joint resistance measurement, pull-off force testing or destructive section analysis, depending on the product's function and customer requirements.

Temperature-rise or environmental testing should be applied when required by the component qualification plan. These tests need defined current, contact force, ambient conditions, duration, and acceptance limits; results without test conditions are not sufficient for engineering comparison.

Quality Documentation and Traceability
For applicable automotive projects, PPAP Level 3 documentation can be prepared according to the customer-specific submission requirements and the agreed quality plan. The package may include:

Process flow diagram.
PFMEA and control plan.
Material certificates.
Dimensional inspection results.
Applicable coating and joining records.

Process capability data where required and supported by sufficient production data.

 

 

 

 

For a new energy fuse project, provide the component drawing and material requirements before tooling or production approval. Apollo can review copper outer caps, brass inner caps, and custom-formed fuse caps against the required geometry, surface treatment, and inspection criteria.

 

Submit your 2D drawing in .DWG or PDF format, your 3D model in STEP format, or a technical specification that identifies material grade, thickness, critical dimensions, plating type, assembly interface, and annual demand.

 

A complete inquiry allows the engineering team to assess forming feasibility, tooling considerations, inspection requirements, and quotation scope. A preliminary DFM review within 24 hours can be requested for complete, clearly specified projects; response time depends on drawing complexity and available engineering information.