Mark Kinder, engineer, Plastic Design Corporation (PDC)
Finally, there is a book on micro moulding! I very much looked forward to receiving a copy of this. The subject of micro moulding is covered in comprehensive detail, supported by documented research and results. However, one should bear in mind that this book is not an overview or introduction to micro moulding. Rather, it takes an in-depth look at the science and technology that can be applied to move the micro moulding industry forward.
The book is divided into four parts, namely:
- Part 1—Polymer Materials and Process Micro Technology;
- Part 2—Tooling Technologies for Micro Mold Making;
- Part 3—Micro Molding Key-Enabling Technologies; and
- Part 4—Multimaterial Micro Processing.
Dr Guido Tosello acknowledges co-authors for the various chapters and carefully cites references for all information contained in the book.
Polymer Materials and Process Micro Technology
Part 1 takes the reader through the adaptation of macro moulding equipment for micro moulding, looking first of all at patent data relating to micro moulding. This is followed by detailing of sensor technology, data acquisition and process monitoring requirements for the micro scale.
Chapter 3—entitled Polymer Material Structure and Properties in Micro Injection Molded Parts—may well be the most important chapter in terms of understanding the difference between micro moulding and conventional macro moulding. The various considerations in scaling are studied, including shear rates, thermal properties, mechanical properties and molecular orientation of both amorphous and semi-crystalline polymers. Additionally, filler materials and their effect on micro moulding are discussed. Key takeaways from this chapter include the significantly different behaviour of the polymer if processed in thin cross sections and the often large difference in final mechanical properties of the moulded part.
Also worthy of note, Chapter 4—Surface Replication in Micro Injection Molding—does an excellent job of defining and quantifying surface replication, supported by a raft of case studies and data.
Tooling Technologies for Micro Mold Making
In Part 2, the construction of the mould is looked into by comparing the process flow for direct and indirect mould fabrication. Various micromachining processes for the direct mould fabrication process are explained, although only two pages are devoted to indirect mould fabrication.
Surface treatment of the mould surface is evaluated. One experiment, using a diamond-like carbon (DLC) coating, produced impressive results in reduction of the demoulding force. Specifically, in the case of moulding acrylonitrile butadiene styrene (ABS), the reduction in demoulding force was 40 percent, and in polycarbonate (PC), it was 16 percent. Unfortunately, the author expressed concern over the long-term failure of the coating. Theoretical and computer aided engineering (CAE) calculations are used to highlight this potential failure mode, although no empirical data is shown.
Next, a study in surface texturing is presented. In the moulding of a polypropylene (PP) part, micro surface texturing is shown to have reduced demoulding force by an average of 15.8 percent over untreated steel. These results are a little confusing as the micro surface texture is an amorphous hydrogenated carbon (aC:H) coating, a type of DLC coating.
Micro Molding Key-Enabling Technologies
Part 3 begins by looking at vacuum-assisted micro injection moulding and its use in a variety of applications. Its many benefits are carefully analysed and well-demonstrated.
Following on from this, computer modelling and simulation of the micro moulding process is explored. The limitations of simulation in the micro moulding world are noted and explained. Accompanying case studies focus on meso parts with micro features.
In chapter 10—Metrological Quality Assurance in Micro Injection Molding—the problems of scale are brought to light. Obtaining discernable measurements of micro features requires the use of metrology instruments affording the necessary resolution. The limitations of traditional metrology instruments, such as insufficient resolution, as well as variation in surface topographies can create a high level of uncertainty in measurement and are therefore highlighted as key considerations. Suitable high-end solutions—for example, atomic force microscopy (AFM) and scanning electron microscopy (SEM)—are explained.
Next, specialised optical instruments, namely the confocal microscope and the interferometer, are described and illustrated. A comparison case study for coordinate measuring machines and optical coordinate measuring machines is presented. A quick mention is made of computed tomography (CT) scanning technology.
Concluding part 3, a look is taken at the current state of play for additive manufacturing (AM). The rate of improvement for the resolutions of various AM technologies means that they may soon be classed as viable for micro moulding applications.
Multimaterial Micro Processing
Part 4 focuses on micro powder injection moulding, both metal and ceramic. The final topic covered, multi-material moulding, is especially important for micro moulding. Unfortunately, all the data presented, bar that of one case study, is for macro moulded parts.
The verdict
So, should this book be on your bookshelf? That depends mostly on what you do and what type of information you need. The information presented is academic, being mostly organised research that has occurred over the last fifteen years in Europe. For researchers, much of this information may be familiar, but having it organised in such a way may indeed spark the next idea. Also, engineers actively involved in micro mechanical design may find food for thought in their design of micro polymer components and areas to test carefully. However, those involved in production micro moulding may find this book somewhat frustrating. Many of the issues encountered in production micro moulding are discussed and research into these areas is presented, but most of the conclusions are open-ended and lack definitive solutions.
Personally, I find myself both excited and frustrated by the material presented. I am excited because the topics explore the everyday issues I encounter. All topics, and the research undertaken, are detailed and well organised. I am frustrated because the technologies presented are described as necessary for successful micro moulding—and they are—but most chapters focus on their limitations. I would like to have seen material presented on overcoming the limitations and applying the information presented. For example, chapter 3.3 covers pressure, specific volume and material temperature (pvT) properties. The relationship between glass transition temperature (Tg) and pressure is noted, but the importance of using pressure change to force solidification is not mentioned. Also, the discussion of CAE simulations in chapter 9.4 makes no mention of pack analysis or warpage analysis.
As previously alluded to, the most disappointing material is in part 4. All of the geometric and rheologic conditions that make micro moulding unique are known to make multi-material moulding much more challenging. This topic is of significant importance to anyone involved in multi-material micro moulding. The experiments are well-designed and the data collected is extensive, but moulding a part that has a 4 by 10 mm cross section has little relevance to micro moulding.
As a technologist, I see value in knowledge when it is applied. That said, will this book remain on my bookshelf? Absolutely!