During the manufacturing of electroacoustic products such as car audio systems, Bluetooth speakers and smart speakers, the figure-eight glue process — the dispensing of adhesive for fixing voice coil leads — serves as a critical procedure determining product reliability and sound quality performance. Figure-eight glue (also known as lead adhesive, wire adhesive, marking glue, eyebrow glue, eyelet glue or black coating) functions primarily to firmly attach voice coil leads to the diaphragm and prevent lead breakage when speakers vibrate under high power. Nevertheless, this seemingly simple process has long been a pain point in quality control for numerous electroacoustic manufacturers.

Breakage of voice coil lead wires is one of the most common failure modes of loudspeakers. When a loudspeaker vibrates violently under high power, if the voice coil lead wires are not firmly fixed or insufficiently covered by adhesive, the leads are prone to fatigue fracture due to repeated tension, which directly results in no sound output or severe deterioration of sound quality. Industry statistics show that lead wire breakage accounts for a considerable proportion of loudspeaker failures, serving as a core bottleneck restricting product reliability.

Manufacturers are confronted with far more difficulties in actual production on the production line:

• Unstable yield rate: Manual dispensing relies on operators’ experience and visual inspection, leading to inconsistent adhesive volume and offset dispensing positions. Although automotive loudspeakers have relatively ample installation space, they impose extremely strict reliability requirements. Continuous vibration and alternating cold and heat during vehicle operation demand one-time qualified fixation of lead wires. Any slight uneven adhesive amount or position deviation may turn into hidden reliability risks during long-term service. Bluetooth speakers and smart speakers feature diverse models and shapes. It becomes harder to guarantee consistent quality of manual dispensing during frequent production changeovers. If the lead wire fixing point deviates from the designed position, the diaphragm will vibrate unbalancedly, followed by problems such as higher distortion rate and shifted frequency response curve.

• High rework cost: Defective products require rework: dissolving the fixing adhesive with solvent, pulling out lead wires for re-soldering, and performing dispensing and fixation again. This process is labor-intensive. Moreover, the diaphragm or voice coil can be easily damaged during secondary operation, causing scrapping of the entire loudspeaker unit.

• Human-dependent production capacity: Manual dispensing is slow and highly dependent on skilled workers. Long training cycles for new employees and high staff turnover cause obvious fluctuations in production capacity, making it difficult to meet demands for stable mass delivery.

Why is the figure-eight gluing process so challenging? The root cause lies in multiple stringent requirements inherent to the process itself.

• Specific routing requirements: The voice coil lead wire cannot be stretched straight. Sufficient curved allowance must be reserved on the diaphragm. The industry best practice is to route the lead wire in an S-shape along the paper cone or form a semicircle on the cone section of the diaphragm. This ensures the lead wire will not be fully stretched when the speaker operates at maximum amplitude. Accordingly, the dispensing position must be accurately placed on a specific curved segment of the lead wire to secure the wire without restricting its vibration allowance, which imposes extremely high standards on dispensing path planning.

• Specifications for adhesive appearance: Figure-eight gluing has strict standards for adhesive status: no stringing, no sagging, and full adhesive beads. Adhesive stringing may bridge the voice coil gap and cause burnout of the voice coil after power-on. Adhesive sagging contaminates the effective vibration area of the diaphragm and alters its vibrating mass. Insufficient adhesive results in weak fixation and frequent lead wire breakage.

• Complex material compatibility: Speaker diaphragms are made of various materials, including paper cones, PP cones, metal cones and composite fiber cones. Different materials have vastly different permeability and adhesion properties with adhesives. The adhesive must be non-penetrative; it should not seep into diaphragm fibers and cause hardening and brittleness. Otherwise, the diaphragm generates distortion under split vibration and may even crack at the coated area in severe cases.

• Unavoidable incoming part tolerances: Speaker workpieces feature positional tolerances and individual variations. Traditional positioning methods relying on precision fixtures fail to implement adaptive compensation, so the equipment must be equipped with visual recognition and dynamic compensation capabilities.

To address the above pain points and technical difficulties, Songqi Intelligent Figure-8 Glue / Lead Wire Glue Vision Tracking Dispensing Machine delivers an intelligent "eye-hand coordination" solution for the figure-8 glue process.

The equipment adopts a high-frame-rate CCD vision system to identify the precise position and posture of speakers on the production line in real time. The control system then drives the dispensing head to dynamically follow the moving path of workpieces. Glue is accurately applied along the outer diameter of the voice coil at the outlet of voice coil leads to fully encapsulate the root of the leads. Workpieces do not need to stop during the whole process, enabling genuine in-line assembly line operation.

Working Process

Incoming material conveying → Vision positioning (identify voice coil position, lead wire direction and diaphragm posture) → Dynamic tracking (real-time tracking of assembly line speed and synchronous tracking of workpiece movement) → Precision dispensing (apply figure-8 glue along lead outlets according to preset paths) → Inspection and curing

Applicable Products

A full range of electroacoustic products including car audio speakers, Bluetooth audio loudspeakers, smart audio units, multimedia speakers and portable audio devices.

Visual Positioning & Accurate Recognition: The built-in vision system automatically identifies the precise position, angle and posture of speakers on the conveyor belt with sub-pixel positioning accuracy. No precision fixtures are required. Products can be placed arbitrarily on the production line, and the vision system automatically completes positioning and deviation correction.

Dynamic Tracking & Non-stop Operation: With multi-axis linkage and precise control of the conveyor belt, the dispensing head tracks the moving speed of workpieces in real time to realize rotating dynamic dispensing without line stoppage. The efficiency of a single machine is several times higher than manual operation, greatly boosting production capacity.

Four-axis Linkage for Complex Curved Surfaces: A rotary axis is added on the basis of traditional three-axis configuration, enabling adaptive processing of complex curved surfaces such as speaker cone diaphragms. From miniature smart speaker units to large vehicle subwoofers, the equipment automatically adapts to products of different sizes and shapes via vision recognition, achieving true "quick changeover for immediate production".

Integrated Vision and Motion Control for Rapid Response: Vision and motion control are deeply integrated into one controller, eliminating communication latency between the vision system and motion system and significantly improving interaction speed and real-time responsiveness.

Traceable Data: Dispensing parameters (glue volume, speed, position, temperature, etc.) are monitored and recorded in real time. Connection with MES systems is supported to provide complete data support for quality traceability and process optimization.

Q1: What is figure-8 adhesive? Why is it named so?

Figure-8 adhesive (also known as lead adhesive, wire adhesive, marking adhesive, eyebrow adhesive, eyelet adhesive or black lacquer) is a special adhesive used to fix voice coil lead wires in loudspeaker manufacturing. It gets its name because it is applied in a figure-8 shape to wrap the root of lead wires. Its main function is to prevent lead wires from fatigue fracture when the loudspeaker vibrates under high power.

Q2: What advantages does the vision tracking dispensing machine have compared with manual dispensing?

Equipped with CCD vision, the vision tracking dispensing machine identifies the position and posture of workpieces in real time and automatically performs dispensing following the speed of the assembly line. Compared with manual dispensing, its advantages are as follows:

1. No production line halt required for higher efficiency;
2. Precise glue volume and consistent dispensing position for more stable yield;
3. No reliance on skilled workers, so production capacity will not be affected by staff turnover;
4. No precision fixtures needed for faster product changeover.

Q3: What products are compatible with your vision tracking dispensing machine?

It is applicable to dispensing for fixing voice coil lead wires of a full range of electroacoustic products, including car audio loudspeakers, Bluetooth speaker drivers, smart speaker units, multimedia speakers and portable audio devices.

Q4: Can the equipment work with diaphragms made of different materials?

Yes. The equipment supports various diaphragm materials such as paper cones, PP cones, metal cones and composite fiber cones. Its vision system can automatically adapt dispensing paths and parameters according to different products.

Q5: Do workpieces need to stop on the production line for vision tracking dispensing?

No. Adopting dynamic tracking technology, the equipment tracks the assembly line speed and workpiece movement in real time, enabling accurate dispensing without stopping workpieces.