Die for crimping ferrules: how to choose and use correctly

Crimping the lugs is a key operation when installing electrical wiring in a car, which guarantees reliable contact and protection against oxidation. Without the right tools, even quality wires and lugs can cause problems ranging from overheating to short circuits. The central element of this process is crimping die — a replaceable working body of the crimper, which determines the shape, compression force and compatibility with the types of tips.

In this article, we will look at what matrices there are, how to select them for specific tasks (from thin signal wires to power cables), and why universal attachments often lose out to specialized ones. You will also find step-by-step instructions for crimping, taking into account common mistakes, a size compatibility table and tips for caring for the tool. We will pay special attention automotive electrics, where the requirements for connection reliability are higher than in the domestic sphere.

What is a crimping die and how does it work?

The matrix is a pair of metal jaws with profiled grooves that compress the ferrule around the wire, creating a permanent connection. Unlike soldering, crimping requires no heat, maintains the wire's flexibility, and is resistant to vibration—critical for automotive wiring. The shape of the notches depends on the type of tip:

• 🔹 Ring (N) — for bolted connections (ground, battery terminals).
• 🔹 Fork (F) — for detachable contacts (relays, fuses).
• 🔹 Tubular (O) - for sleeves and stranded wires.
• 🔹 Isolated (I) - with a plastic cuff that also compresses the insulation.

When compressed, the matrix deforms the metal of the tip, “pressing” it into the wire cores. A high-quality matrix ensures uniform force over the entire area, eliminating microcracks. Cheap bits often have burrs or inaccurate geometry, resulting in false crimp - when the connection looks normal, but under load it heats up or falls off.

In automotive electrics, matrices for tips with a cross-section from 0.5 mm² (sensors, signal wires) up to 16 mm² (starter cables). To work with aluminum wires, special dies with an increased radius of curvature are required - aluminum is more fragile than copper.

Types of matrices: universal vs specialized

All matrices are divided into two large groups: universal (with adjustable gap) and specialized (for a specific tip type/size). The first are convenient for one-time work, but lose in accuracy. The latter provide ideal crimping, but require replaceable nozzles.

Matrix type	Benefits	Disadvantages	Application
Universal (adjustable)	One tool for several sizes, budget price	Inaccurate crimping, rapid wear, risk of tip damage	Occasional work, household electrical
Specialized (fixed)	Ideal crimp geometry, long service life	Expensive, you need attachments for every size	Professional installation, auto electrician
For insulated tips	Crimping + melting of insulation in one stroke	Requires precise selection of tip color	Signal circuits, sensors
For aluminum wires	Soft compression without microcracks	Not suitable for copper, high price	Power circuits (for example, winch power)

Ideal for automotive work combined approach: universal matrix for rare sizes (for example, 0.35 mm² for ABS sensors) and specialized attachments for frequently used ones (for example, 1.5 mm² for lighting, 6 mm² for the starter).

⚠️ Attention: Dies for insulated tips not interchangeable with ordinary ones! An attempt to crimp an insulated tip with a standard die will damage the plastic collar and cause unreliable contact.

How to choose a matrix: 5 key parameters

When choosing a matrix, focus on:

1. Material: Optimal chrome vanadium steel (labeling Cr-V) or hardened tool steel. Avoid silumin - it crumbles after 50-100 crimps.
2. Standard sizes: Check compatibility with your wire size. For example, for a car audio system you will need matrices for 0.75–2.5 mm².
3. Jaw profile: For ring tips, select dies with trapezoidal profile (better grips the wire), for fork ones - with rectangular.
4. Fastening: Make sure the die fits your crimper. Popular Standards - 180° (for hand tools) and 90° (for hydraulic ones).
5. Manufacturer: Market leaders - Knipex, Weidmüller, HTC. Budget brands (Jonnesway, Stayer) are suitable for occasional use.

To work with stranded wires (typical for cars) it is important that the matrix has stepped profile — it prevents individual cores from being squeezed out. For example, matrices Knipex 97 52 03 are specially designed for automotive wiring and are marked AWG (American standard sections).

Material marking available (Cr-V, HSS, etc.)|

The profile of the jaws corresponds to the type of tips (N/F/O)|

There is a margin of force (minimum 20% of the required)|

Compatible with your crimper (check mount)|

Comes with replacement tips for popular sizes -->

Step-by-step instructions: how to crimp a tip with a matrix

The crimping process seems simple, but 80% of car electrical problems are caused by errors at this stage. Follow the algorithm:

1. Wire preparation:
   • 🔹 Remove the insulation for the length of the tip sleeve (use stripper, not a knife!).
   • 🔹 Twist the wires clockwise and tin with solder (optional for copper).
   • 🔹 Put on the heat shrink tube up to crimping, if provided.
2. Nozzle selection:
   • 🔹 Select the matrix according to tip insulation color (standard: red - 0.5–1.5 mm², blue - 1.5–2.5 mm², yellow - 4–6 mm²).
   • 🔹 Check that the die number matches the marking on the tip (for example, N-2.5).
3. Crimping:
   • 🔹 Insert the tip into the matrix all the way — the protrusion on the jaws should fix its position.
   • 🔹 Squeeze the crimper handles smoothly, without jerking. For hydraulic tools, it should take 2-3 seconds to build up pressure.
   • 🔹 After crimping, check the connection for stretching — high-quality crimping can withstand a force of 3–5 kg.

Isolation:

• 🔹 Slide the heat shrink tube onto the crimping area and heat it with a hairdryer (temperature 120–150°C).
• 🔹 For additional protection, use electrical tape 3M Scotch 2228 or liquid insulation.

Critical error - underpressure or pinch. In the first case, the contact will heat up, in the second, the wire strands will break. Optimal crimp force for copper: 8–12 kN (depending on the section). For control use dynamometer crimper or rely on the “click” of the ratchet mechanism.

What happens if you crimp an aluminum wire with a copper matrix?
Aluminum is softer than copper, and the standard matrix deforms its structure too much, creating microcracks. This leads to:
1. Local overheating (due to increased resistance in cracks).
2. Contact oxidation (aluminum reacts actively with oxygen).
3. Loss of mechanical strength (the wire may break off due to vibration).

For aluminum, use marked dies Al or Cu/Al and special contact paste (for example, Alu-Plus).